/* ==========================================================================
   ACADEMIC DEVELOPER DOCUMENTATION - CHAPTER & LESSON PAGES
   Soft Light Theme | Calm | High Readability
   ========================================================================== */

/* Layout & Main Container (~1400px overall width) */
.lesson-page {
    max-width: 1400px;
    margin: 0 auto;
    padding: 32px 32px 80px 320px;
    box-sizing: border-box;
    width: 100%;
}

/* Base navigation transition on study subpages */
body.is-lesson-page .nevigation {
    transition: all 0.35s cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================================================
   SCROLLED / SHRUNKEN NAVIGATION ON LEFT (Docks above index sidebar)
   ========================================================================== */

body.is-lesson-page .nevigation.is-scrolled {
    position: fixed;
    top: 0;
    left: max(32px, calc((100vw - 1400px) / 2 + 32px));
    width: 260px;
    height: 56px;
    padding: 0 16px;
    border-radius: 0 0 var(--radius-md) var(--radius-md);
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-top: none;
    box-shadow: 0 4px 16px rgba(23, 32, 51, 0.08), 0 1px 3px rgba(23, 32, 51, 0.04);
    z-index: 1100;
    margin: 0;
    cursor: pointer;
    box-sizing: border-box;
}

body.is-lesson-page .nevigation.is-scrolled .logo {
    font-size: 15px;
    flex-direction: row;
    align-items: center;
    justify-content: space-between;
    width: 100%;
}

body.is-lesson-page .nevigation.is-scrolled .logo::after {
    display: none;
}

body.is-lesson-page .nevigation.is-scrolled .nav-links {
    display: none;
}

/* Dropdown Arrow Indicator in Logo */
.nav-dropdown-indicator {
    display: none;
    font-size: 12px;
    color: var(--accent-purple);
    transition: transform 0.25s ease;
    background: var(--purple-light);
    width: 22px;
    height: 22px;
    border-radius: 50%;
    align-items: center;
    justify-content: center;
}

body.is-lesson-page .nevigation.is-scrolled .nav-dropdown-indicator {
    display: inline-flex;
}

body.is-lesson-page .nevigation.is-scrolled:hover .nav-dropdown-indicator,
body.is-lesson-page .nevigation.is-scrolled .nav-scrolled-dropdown.touch-active ~ .logo .nav-dropdown-indicator {
    transform: rotate(180deg);
}

/* Dropdown Menu on Shrunken Nav */
.nav-scrolled-dropdown {
    display: flex;
    flex-direction: column;
    gap: 4px;
    position: absolute;
    top: calc(100% + 8px);
    left: 0;
    width: 100%;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    box-shadow: 0 12px 32px rgba(23, 32, 51, 0.12), 0 2px 6px rgba(0, 0, 0, 0.04);
    padding: 8px;
    box-sizing: border-box;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    transition: all 0.25s cubic-bezier(0.16, 1, 0.3, 1);
    pointer-events: none;
    z-index: 1200;
}

body.is-lesson-page .nevigation.is-scrolled:hover .nav-scrolled-dropdown,
body.is-lesson-page .nevigation.is-scrolled .nav-scrolled-dropdown.touch-active {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
    pointer-events: auto;
}

.dropdown-header {
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.8px;
    color: var(--text-muted);
    padding: 6px 10px 4px 10px;
}

.dropdown-link {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 8px 12px;
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 13.5px;
    font-weight: 500;
    border-radius: var(--radius-sm);
    transition: all 0.15s ease;
}

.dropdown-link:hover {
    background: var(--purple-light);
    color: var(--accent-purple);
}

.dropdown-link.active {
    background: var(--purple-light);
    color: var(--accent-purple);
    font-weight: 600;
}

.dropdown-icon {
    font-size: 14px;
    line-height: 1;
}

/* ==========================================================================
   HERO HEADER SECTION & STICKY MORPHING
   ========================================================================== */

/* Hero Spacer to prevent content jump when banner sticks */
.chapter-hero-spacer {
    display: none;
    height: 180px;
    margin-bottom: 28px;
}

.chapter-hero-spacer.active {
    display: block;
}

.chapter-hero-banner {
    background: var(--purple-light);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 36px 44px;
    margin-bottom: 28px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    position: relative;
    overflow: hidden;
    width: 100%;
    box-sizing: border-box;
    transition: all 0.35s cubic-bezier(0.16, 1, 0.3, 1);
}

.chapter-hero-content {
    max-width: 720px;
    z-index: 2;
}

.chapter-hero-tag {
    color: var(--accent-purple);
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1.2px;
    margin-bottom: 6px;
    display: inline-block;
    transition: all 0.25s ease;
}

.chapter-hero-title {
    color: var(--text-primary);
    font-size: 38px;
    font-weight: 800;
    letter-spacing: -1px;
    margin: 0 0 10px 0;
    line-height: 1.2;
    transition: all 0.25s ease;
}

.chapter-hero-title .accent-text {
    color: var(--accent-purple);
}

.chapter-hero-desc {
    color: var(--text-secondary);
    font-size: 16px;
    line-height: 1.6;
    margin: 0 0 18px 0;
    transition: all 0.25s ease;
}

.chapter-hero-pills {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
    transition: all 0.25s ease;
}

.chapter-hero-pill {
    background: #FFFFFF;
    color: var(--accent-purple);
    border: 1px solid var(--border-color);
    padding: 4px 14px;
    border-radius: var(--radius-pill);
    font-size: 12.5px;
    font-weight: 600;
    transition: all 0.25s ease;
}

.chapter-hero-icon-art {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 140px;
    height: 120px;
    background: rgba(108, 76, 232, 0.12);
    border-radius: 20px;
    color: var(--accent-purple);
    font-size: 44px;
    font-weight: 800;
    font-family: 'JetBrains Mono', monospace;
    user-select: none;
    flex-shrink: 0;
    transition: all 0.3s cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================================================
   STICKY MORPHED PURPLE CHAPTER HEADER BAR
   ========================================================================== */

.chapter-hero-banner.is-sticky {
    position: sticky;
    top: 0;
    width: 100%;
    max-width: 100%;
    height: 54px;
    min-height: 54px;
    padding: 0 24px;
    margin-bottom: 24px;
    border-radius: 0 0 var(--radius-md) var(--radius-md);
    background: #F0EBFF;
    background-color: #F0EBFF;
    opacity: 1;
    backdrop-filter: none;
    -webkit-backdrop-filter: none;
    border: 1px solid rgba(108, 76, 232, 0.25);
    border-top: none;
    box-shadow: 0 4px 16px rgba(108, 76, 232, 0.08), 0 1px 3px rgba(23, 32, 51, 0.04);
    z-index: 1090;
    display: flex;
    align-items: center;
    justify-content: space-between;
    box-sizing: border-box;
}

.chapter-hero-banner.is-sticky .chapter-hero-content {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    max-width: 100%;
    gap: 16px;
}

.chapter-hero-banner.is-sticky .chapter-hero-tag {
    font-size: 13px;
    font-weight: 700;
    color: var(--accent-purple);
    background: #FFFFFF;
    border-radius: var(--radius-pill);
    border: 1px solid rgba(108, 76, 232, 0.2);
    padding: 4px 14px;
    margin-bottom: 0;
    flex-shrink: 0;
    white-space: nowrap;
    text-transform: none;
    letter-spacing: 0.2px;
}

.chapter-hero-banner.is-sticky .chapter-hero-title {
    font-size: 16.5px;
    font-weight: 700;
    letter-spacing: -0.2px;
    color: var(--text-primary);
    margin: 0;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    line-height: 1.2;
    text-align: right;
}

.chapter-hero-banner.is-sticky .chapter-hero-desc {
    display: none;
}

.chapter-hero-banner.is-sticky .chapter-hero-pills {
    display: none;
}

.chapter-hero-banner.is-sticky .chapter-hero-icon-art {
    display: none;
}

/* Main Lesson Card & Container */
.lesson-page .lesson-container,
.lesson-container {
    display: block;
    width: 100%;
    max-width: 100%;
}

.lesson-page .lesson-card,
.lesson-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-card);
    padding: 44px 48px;
    width: 100%;
    max-width: 100%;
    box-sizing: border-box;
    text-align: left;
    display: block;
}

.lesson-page .lesson-card:hover {
    transform: none;
    box-shadow: var(--shadow-card);
    border-color: var(--border-color);
}

/* Chapter Top Action Bar */
.chapter-top-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 24px;
    padding-bottom: 18px;
    border-bottom: 1px solid var(--border-color);
    gap: 16px;
    width: 100%;
}

.top-nav-meta {
    display: flex;
    align-items: center;
    gap: 12px;
}

.top-nav-actions {
    display: flex;
    align-items: center;
    gap: 10px;
}

.back-to-js-link {
    color: var(--accent-purple);
    text-decoration: none;
    font-size: 13.5px;
    font-weight: 600;
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 6px 14px;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-pill);
    transition: all 0.15s ease;
}

.back-to-js-link:hover {
    background: var(--purple-light);
    border-color: var(--accent-purple);
}

.chapter-badge {
    color: var(--accent-purple);
    font-size: 13px;
    font-weight: 600;
    background: var(--purple-light);
    border: 1px solid rgba(108, 76, 232, 0.2);
    padding: 5px 14px 5px 16px;
    border-radius: var(--radius-pill);
    display: inline-flex;
    align-items: center;
    gap: 6px;
    cursor: pointer;
    font-family: inherit;
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    user-select: none;
    outline: none;
}

.chapter-badge:hover,
.chapter-badge.is-active {
    background: #E8E0FE;
    border-color: var(--accent-purple);
    box-shadow: 0 2px 10px rgba(108, 76, 232, 0.18);
    transform: translateY(-1px);
}

.chapter-badge-arrow {
    font-size: 11px;
    display: inline-block;
    transition: transform 0.25s cubic-bezier(0.16, 1, 0.3, 1);
}

.chapter-badge.is-active .chapter-badge-arrow {
    transform: rotate(180deg);
}

/* ==========================================================================
   ALL CHAPTERS ANIMATED MODAL DRAWER
   ========================================================================== */

.all-chapters-modal-overlay {
    position: fixed;
    inset: 0;
    background: rgba(15, 23, 42, 0.45);
    backdrop-filter: blur(6px);
    -webkit-backdrop-filter: blur(6px);
    z-index: 9999;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    box-sizing: border-box;
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition: opacity 0.28s cubic-bezier(0.16, 1, 0.3, 1),
                visibility 0.28s cubic-bezier(0.16, 1, 0.3, 1);
}

.all-chapters-modal-overlay.is-open {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
}

.all-chapters-modal {
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: 20px;
    width: 100%;
    max-width: 820px;
    max-height: 86vh;
    display: flex;
    flex-direction: column;
    box-shadow: 0 24px 64px rgba(23, 32, 51, 0.18), 0 4px 16px rgba(108, 76, 232, 0.08);
    transform: scale(0.94) translateY(12px);
    opacity: 0;
    transition: transform 0.32s cubic-bezier(0.16, 1, 0.3, 1),
                opacity 0.28s cubic-bezier(0.16, 1, 0.3, 1);
    overflow: hidden;
    box-sizing: border-box;
}

.all-chapters-modal-overlay.is-open .all-chapters-modal {
    transform: scale(1) translateY(0);
    opacity: 1;
}

/* Modal Header */
.all-chapters-header {
    padding: 20px 24px 16px 24px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: #FAF9FF;
}

.all-chapters-track-tag {
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--accent-purple);
    display: block;
    margin-bottom: 3px;
}

.all-chapters-title {
    font-size: 20px;
    font-weight: 800;
    color: var(--text-primary);
    margin: 0;
    letter-spacing: -0.3px;
}

.all-chapters-close-btn {
    width: 34px;
    height: 34px;
    border-radius: 50%;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    color: var(--text-muted);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 14px;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.2s ease;
}

.all-chapters-close-btn:hover {
    background: var(--purple-light);
    color: var(--accent-purple);
    border-color: var(--accent-purple);
    transform: rotate(90deg);
}

/* Modal Search & Filter */
.all-chapters-search-bar {
    padding: 14px 24px 10px 24px;
    position: relative;
    display: flex;
    align-items: center;
    background: #FFFFFF;
}

.all-chapters-search-icon {
    position: absolute;
    left: 36px;
    font-size: 14px;
    color: var(--text-muted);
    pointer-events: none;
}

.all-chapters-search-input {
    width: 100%;
    height: 42px;
    padding: 0 16px 0 42px;
    border-radius: var(--radius-pill);
    border: 1.5px solid var(--border-color);
    font-size: 14px;
    font-family: inherit;
    color: var(--text-primary);
    background: #F8FAFC;
    transition: all 0.2s ease;
    box-sizing: border-box;
    outline: none;
}

.all-chapters-search-input:focus {
    background: #FFFFFF;
    border-color: var(--accent-purple);
    box-shadow: 0 0 0 3px rgba(108, 76, 232, 0.12);
}

/* Modal Progress Card */
.all-chapters-progress-card {
    margin: 0 24px 12px 24px;
    padding: 12px 16px;
    background: var(--purple-light);
    border: 1px solid rgba(108, 76, 232, 0.18);
    border-radius: var(--radius-md);
}

.all-chapters-progress-labels {
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-size: 12.5px;
    font-weight: 600;
    margin-bottom: 8px;
}

.all-chapters-progress-labels .progress-title {
    color: var(--accent-purple);
}

.all-chapters-progress-labels .progress-stats {
    color: var(--text-secondary);
}

.all-chapters-progress-track {
    height: 6px;
    background: rgba(108, 76, 232, 0.15);
    border-radius: 4px;
    overflow: hidden;
}

.all-chapters-progress-fill {
    height: 100%;
    background: var(--accent-purple);
    border-radius: 4px;
    transition: width 0.4s cubic-bezier(0.16, 1, 0.3, 1);
}

/* Chapters Grid */
.all-chapters-grid {
    padding: 6px 24px 16px 24px;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 10px;
    overflow-y: auto;
    max-height: 48vh;
    scrollbar-width: thin;
    scrollbar-color: rgba(108, 76, 232, 0.3) transparent;
}

.all-chapters-grid::-webkit-scrollbar {
    width: 6px;
}

.all-chapters-grid::-webkit-scrollbar-thumb {
    background: rgba(108, 76, 232, 0.3);
    border-radius: 3px;
}

/* Chapter Item Card */
.all-chapters-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 10px 14px;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    text-decoration: none;
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    box-sizing: border-box;
    position: relative;
}

.all-chapters-item:hover {
    background: #FAF9FF;
    border-color: var(--accent-purple);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(108, 76, 232, 0.1);
}

.all-chapters-item.is-current {
    background: var(--purple-light);
    border-color: var(--accent-purple);
    box-shadow: 0 0 0 1px var(--accent-purple), 0 4px 14px rgba(108, 76, 232, 0.14);
}

.all-chapters-num {
    width: 32px;
    height: 32px;
    border-radius: 8px;
    background: #F1F5F9;
    color: var(--text-secondary);
    font-size: 13px;
    font-weight: 700;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all 0.2s ease;
}

.all-chapters-item:hover .all-chapters-num {
    background: var(--purple-light);
    color: var(--accent-purple);
}

.all-chapters-item.is-current .all-chapters-num {
    background: var(--accent-purple);
    color: #FFFFFF;
}

.all-chapters-details {
    flex: 1;
    min-width: 0;
    display: flex;
    flex-direction: column;
    gap: 2px;
}

.all-chapters-item-title {
    font-size: 13.5px;
    font-weight: 600;
    color: var(--text-primary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    line-height: 1.3;
}

.all-chapters-curr-tag {
    font-size: 11px;
    font-weight: 700;
    color: var(--accent-purple);
}

.all-chapters-done-tag {
    font-size: 11px;
    font-weight: 600;
    color: #10B981;
}

.all-chapters-status {
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
}

.status-check {
    width: 22px;
    height: 22px;
    border-radius: 50%;
    background: #ECFDF5;
    color: #10B981;
    border: 1px solid rgba(16, 185, 129, 0.3);
    font-size: 12px;
    font-weight: 800;
    display: flex;
    align-items: center;
    justify-content: center;
}

.status-circle {
    width: 14px;
    height: 14px;
    border-radius: 50%;
    border: 1.5px solid #CBD5E1;
    display: inline-block;
}

/* Modal Footer */
.all-chapters-footer {
    padding: 14px 24px;
    border-top: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: #FAF9FF;
}

.footer-hint {
    font-size: 12px;
    color: var(--text-muted);
}

.footer-hint kbd {
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: 4px;
    padding: 2px 6px;
    font-size: 11px;
    box-shadow: 0 1px 2px rgba(0,0,0,0.05);
}

.all-chapters-dashboard-link {
    color: var(--accent-purple);
    text-decoration: none;
    font-size: 13px;
    font-weight: 600;
    transition: all 0.15s ease;
}

.all-chapters-dashboard-link:hover {
    text-decoration: underline;
}

@media (max-width: 680px) {
    .all-chapters-grid {
        grid-template-columns: 1fr;
    }
    .all-chapters-modal {
        max-height: 92vh;
    }
}

.top-nav-btn {
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-pill);
    padding: 6px 14px;
    color: var(--text-secondary);
    font-size: 13px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.15s ease;
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

.top-nav-btn:hover {
    border-color: #CBD5E1;
    color: var(--text-primary);
}

.top-nav-btn.bookmark-btn.active {
    background: var(--yellow-light);
    border-color: var(--yellow-border);
    color: #B45309;
    font-weight: 600;
}

.top-nav-btn.complete-btn.active {
    background: var(--teal-light);
    border-color: var(--teal-border);
    color: var(--teal);
    font-weight: 600;
}

/* Headings & Typography inside Lesson Card */
.lesson-card h2 {
    color: var(--text-primary);
    font-size: 28px;
    font-weight: 800;
    letter-spacing: -0.5px;
    margin: 24px 0 12px 0;
    display: flex;
    align-items: center;
    gap: 10px;
    scroll-margin-top: 80px;
}

.lesson-card > h2:first-of-type,
.lesson-card .chapter-main-title {
    font-size: 32px;
    margin-top: 6px;
    scroll-margin-top: 80px;
}

.lesson-card h2::before {
    content: '';
    display: inline-block;
    width: 4px;
    height: 24px;
    background-color: var(--accent-purple);
    border-radius: 2px;
    flex-shrink: 0;
}

.lesson-card h3 {
    color: var(--text-primary);
    font-size: 20px;
    font-weight: 700;
    letter-spacing: -0.3px;
    margin-top: 32px;
    margin-bottom: 10px;
    scroll-margin-top: 80px;
}

.lesson-card h4 {
    color: var(--text-primary);
    font-size: 16px;
    font-weight: 700;
    margin: 0 0 8px 0;
    scroll-margin-top: 80px;
}

.lesson-card p {
    color: var(--text-secondary);
    font-size: 16px;
    line-height: 1.7;
    margin-bottom: 16px;
}

.lesson-card ul, .lesson-card ol {
    color: var(--text-secondary);
    font-size: 15.5px;
    line-height: 1.75;
    margin: 12px 0 20px 24px;
    padding-left: 4px;
}

.lesson-card li {
    margin-bottom: 6px;
}

.lesson-card strong {
    color: var(--text-primary);
    font-weight: 600;
}

.lesson-card inline-code,
.lesson-card p code,
.lesson-card li code,
.lesson-card h2 code,
.lesson-card h3 code,
.lesson-card h4 code {
    background: var(--purple-light);
    color: var(--accent-purple);
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 13.5px;
    padding: 2px 6px;
    border-radius: 4px;
    border: 1px solid rgba(108, 76, 232, 0.15);
}

/* ==========================================================================
   CALLOUT CARDS (Real-World Analogy, Tips, Pitfalls)
   ========================================================================== */

/* 9. Real-World Analogy Card: Soft Yellow */
.analogy-box {
    background: var(--yellow-light);
    border: 1px solid var(--yellow-border);
    border-left: 4px solid var(--yellow);
    border-radius: var(--radius-md);
    padding: 20px 24px;
    margin: 24px 0;
}

.analogy-box h4 {
    color: #92400E;
    font-size: 16px;
    font-weight: 700;
    margin: 0 0 8px 0;
    display: flex;
    align-items: center;
    gap: 8px;
}

.analogy-box p {
    color: var(--text-primary);
    font-size: 15px;
    line-height: 1.65;
    margin: 0;
}

.analogy-box code {
    background: rgba(245, 158, 11, 0.15);
    color: #92400E;
    border-color: rgba(245, 158, 11, 0.3);
}

/* Tip Box: Light Blue */
.tip-box {
    background: var(--blue-light);
    border: 1px solid var(--blue-border);
    border-left: 4px solid var(--blue);
    border-radius: var(--radius-md);
    padding: 20px 24px;
    margin: 24px 0;
}

.tip-box h4 {
    color: #1E40AF;
    font-size: 16px;
    font-weight: 700;
    margin: 0 0 8px 0;
}

.tip-box p {
    color: var(--text-primary);
    font-size: 15px;
    line-height: 1.65;
    margin: 0;
}

/* Pitfall Box: Soft Red */
.pitfall-box {
    background: var(--red-light);
    border: 1px solid var(--red-border);
    border-left: 4px solid var(--red);
    border-radius: var(--radius-md);
    padding: 20px 24px;
    margin: 24px 0;
}

.pitfall-box h4 {
    color: #991B1B;
    font-size: 16px;
    font-weight: 700;
    margin: 0 0 8px 0;
}

.pitfall-box p {
    color: var(--text-primary);
    font-size: 15px;
    line-height: 1.65;
    margin: 0;
}

/* ==========================================================================
   11. CONCEPT CARDS (Dual Phase / Features Cards)
   ========================================================================== */

.concept-cards-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 20px;
    margin: 24px 0;
    width: 100%;
    max-width: 100%;
    box-sizing: border-box;
}

.concept-card {
    background: #FFFFFF !important;
    border: 1px solid var(--border-color, #E2E8F0) !important;
    border-radius: var(--radius-md, 12px) !important;
    padding: 20px 22px !important;
    position: relative;
    display: flex;
    flex-direction: column;
    box-sizing: border-box;
    height: 100%;
    min-width: 0;
    overflow: hidden;
    box-shadow: 0 2px 10px rgba(15, 23, 42, 0.04) !important;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.concept-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 18px rgba(15, 23, 42, 0.08) !important;
}

/* Card Top Border Variations */
.concept-card.teal-card   { border-top: 3.5px solid #10B981 !important; }
.concept-card.blue-card   { border-top: 3.5px solid #3B82F6 !important; }
.concept-card.purple-card { border-top: 3.5px solid #6C4CE8 !important; }
.concept-card.orange-card { border-top: 3.5px solid #F59E0B !important; }
.concept-card.rose-card, .concept-card.red-card { border-top: 3.5px solid #EF4444 !important; }

.concept-card-num {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 800;
    font-size: 13px;
    margin-bottom: 12px;
    flex-shrink: 0;
    background: #6C4CE8;
    color: #FFFFFF;
}

.concept-card.teal-card .concept-card-num   { background: #10B981 !important; color: #FFFFFF !important; }
.concept-card.blue-card .concept-card-num   { background: #3B82F6 !important; color: #FFFFFF !important; }
.concept-card.purple-card .concept-card-num { background: #6C4CE8 !important; color: #FFFFFF !important; }
.concept-card.orange-card .concept-card-num { background: #F59E0B !important; color: #FFFFFF !important; }
.concept-card.rose-card .concept-card-num,
.concept-card.red-card .concept-card-num    { background: #EF4444 !important; color: #FFFFFF !important; }

/* Titles: Clean Dark / Black text */
.concept-card h4 {
    font-size: 15.5px !important;
    font-weight: 700 !important;
    color: var(--text-primary, #0F172A) !important;
    margin: 0 0 4px 0 !important;
    flex-shrink: 0;
    letter-spacing: -0.2px;
}

/* Subtitles: Clean Neutral Text */
.concept-card p.subtitle,
.concept-card > p:first-of-type {
    color: var(--text-muted, #64748B) !important;
    font-size: 13px !important;
    font-weight: 500 !important;
    line-height: 1.45 !important;
    margin: 0 0 10px 0 !important;
    flex-shrink: 0;
}

.concept-card p {
    color: var(--text-secondary, #334155) !important;
    font-size: 13px !important;
    line-height: 1.55 !important;
    margin: 0 0 8px 0;
}

.concept-card ul {
    padding-left: 18px !important;
    margin: 6px 0 10px 0 !important;
    font-size: 13px !important;
    color: var(--text-secondary, #334155) !important;
}

.concept-card li {
    margin-bottom: 6px !important;
    line-height: 1.5 !important;
}

/* Inline code tags inside concept cards: Clean neutral tech badge */
.concept-card :not(pre) > code,
.concept-card p code,
.concept-card li code,
.concept-card > code {
    background: #F1F5F9 !important;
    color: #475569 !important;
    border: 1px solid #E2E8F0 !important;
    padding: 2px 6px !important;
    border-radius: 4px !important;
    font-family: 'JetBrains Mono', Consolas, monospace !important;
    font-size: 12px !important;
    font-weight: 600 !important;
    display: inline-block !important;
}

/* Pre / Code blocks inside concept cards & lesson cards: Transparent background and crisp light text */
.concept-card pre code,
.concept-card .code-box code,
.concept-card .code-block-wrapper code,
.code-box code,
.code-box pre code,
.lesson-card pre code,
pre code {
    background: transparent !important;
    color: #F8FAFC !important;
    border: none !important;
    padding: 0 !important;
    border-radius: 0 !important;
    box-shadow: none !important;
    display: block !important;
    font-family: 'JetBrains Mono', Consolas, Monaco, "Courier New", monospace !important;
    font-size: 12.5px !important;
    line-height: 1.55 !important;
}

.concept-card pre,
.concept-card .code-block-wrapper {
    margin-top: auto;
    margin-bottom: 0;
    width: 100%;
    background: #1E293B !important;
    color: #F8FAFC !important;
    border-radius: 6px !important;
    overflow-x: auto;
}

/* Inline SVG Diagram Boxes */
.diagram-box {
    background: #FAFBFC;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 24px 20px;
    margin: 24px 0;
    text-align: center;
    overflow-x: auto;
}

.diagram-box svg {
    max-width: 100%;
    height: auto;
    display: block;
    margin: 0 auto;
}

.diagram-title {
    color: var(--text-secondary);
    font-size: 13px;
    font-weight: 600;
    margin-top: 14px;
    letter-spacing: 0.3px;
    text-transform: uppercase;
}

/* ==========================================================================
   4. SIDEBAR - TABLE OF CONTENTS & PROGRESS SYSTEM
   ========================================================================== */

.page-index-sidebar {
    position: fixed;
    top: 90px;
    left: max(32px, calc((100vw - 1400px) / 2 + 32px));
    width: 260px;
    max-height: calc(100vh - 110px);
    overflow-y: auto;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 20px 16px;
    box-shadow: var(--shadow-card);
    z-index: 999;
    box-sizing: border-box;
    display: flex;
    flex-direction: column;
    transition: top 0.35s cubic-bezier(0.16, 1, 0.3, 1), max-height 0.35s cubic-bezier(0.16, 1, 0.3, 1), width 0.35s ease, left 0.35s ease;
}

.page-index-sidebar.nav-scrolled {
    top: 72px;
    max-height: calc(100vh - 88px);
}

.page-index-sidebar::-webkit-scrollbar {
    width: 4px;
}

.page-index-sidebar::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 4px;
}

.index-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 14px;
    padding-bottom: 12px;
    border-bottom: 1px solid var(--border-color);
    flex-shrink: 0;
}

.index-title {
    color: var(--text-primary);
    font-size: 14.5px;
    font-weight: 700;
    letter-spacing: -0.2px;
}

.sidebar-js-btn {
    color: var(--accent-purple);
    text-decoration: none;
    font-size: 11.5px;
    font-weight: 600;
    padding: 3px 10px;
    background: var(--purple-light);
    border: 1px solid rgba(108, 76, 232, 0.2);
    border-radius: var(--radius-pill);
    transition: all 0.15s ease;
}

.sidebar-js-btn:hover {
    background: var(--accent-purple);
    color: #FFFFFF;
}

.index-list {
    list-style: none;
    padding: 0;
    margin: 0;
    flex: 1;
    overflow-y: auto;
}

.index-item {
    margin-bottom: 2px;
}

.index-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 13px;
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 6px 10px;
    border-radius: var(--radius-sm);
    transition: all 0.15s ease;
    line-height: 1.35;
    word-break: break-word;
    border-left: 3px solid transparent;
}

.index-link .index-bullet {
    color: var(--text-muted);
    font-size: 7px;
    line-height: 1;
    flex-shrink: 0;
    transition: all 0.15s ease;
}

.index-link.is-h3 {
    padding-left: 18px;
    font-size: 12px;
    color: var(--text-muted);
}

.index-link:hover {
    color: var(--text-primary);
    background: var(--bg-primary);
}

.index-link:hover .index-bullet {
    color: var(--accent-purple);
}

.index-link.active {
    color: var(--accent-purple);
    font-weight: 600;
    background: var(--purple-light);
    border-left: 3px solid var(--accent-purple);
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

.index-link.active .index-bullet {
    color: var(--accent-purple);
}

/* 7. Sidebar Progress Card */
.sidebar-progress-card {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 14px;
    margin-top: 14px;
    flex-shrink: 0;
}

.sidebar-progress-title {
    color: var(--text-primary);
    font-size: 13px;
    font-weight: 700;
    margin-bottom: 2px;
}

.sidebar-progress-stats {
    color: var(--text-muted);
    font-size: 12px;
    margin-bottom: 8px;
}

.sidebar-progress-row {
    display: flex;
    align-items: center;
    gap: 8px;
}

.sidebar-progress-track {
    flex: 1;
    height: 8px;
    background: var(--border-color);
    border-radius: var(--radius-pill);
    overflow: hidden;
}

.sidebar-progress-fill {
    height: 100%;
    background: var(--accent-purple);
    border-radius: var(--radius-pill);
    transition: width 0.3s ease;
}

.sidebar-progress-percent {
    color: var(--text-primary);
    font-size: 12px;
    font-weight: 700;
    min-width: 28px;
    text-align: right;
}

/* Sidebar Quote Card */
.sidebar-quote-card {
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 10px 12px;
    margin-top: 10px;
    display: flex;
    align-items: flex-start;
    gap: 8px;
    flex-shrink: 0;
}

.sidebar-quote-icon {
    color: var(--accent-purple);
    font-size: 16px;
    line-height: 1;
    user-select: none;
}

.sidebar-quote-text {
    color: var(--text-secondary);
    font-size: 12px;
    line-height: 1.45;
    font-style: italic;
    margin: 0;
}

/* ==========================================================================
   DOM PLAYGROUND & CHEAT SHEET STYLES
   ========================================================================== */

.dom-playground {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
    margin: 24px 0;
}

.playground-editor,
.playground-preview {
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 20px;
    display: flex;
    flex-direction: column;
}

.preview-label {
    color: var(--accent-purple);
    font-size: 11.5px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1px;
    margin: 0 0 12px 0;
}

.legacy-dom-box {
    width: 110px;
    height: 110px;
    background: var(--accent-purple);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    color: #FFFFFF;
    font-weight: 700;
    font-size: 13px;
    margin: 16px 0;
    transition: all 0.3s ease;
    box-shadow: 0 6px 16px rgba(108, 76, 232, 0.2);
}

.dom-cycle {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 8px;
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 18px 20px;
    margin: 20px 0;
    flex-wrap: wrap;
}

.cycle-box {
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 8px 14px;
    color: var(--text-primary);
    font-size: 13.5px;
    font-weight: 600;
}

.cycle-arrow {
    color: var(--accent-purple);
    font-weight: 800;
    font-size: 18px;
}

.cheat-sheet {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 12px;
    margin: 20px 0;
}

.cheat-sheet div {
    display: flex;
    flex-direction: column;
    gap: 4px;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 12px 14px;
}

.cheat-sheet code {
    color: var(--accent-purple);
    font-family: 'JetBrains Mono', monospace;
    font-size: 13.5px;
    font-weight: 600;
}

.cheat-sheet span {
    color: var(--text-secondary);
    font-size: 13px;
}

/* ==========================================================================
   SIDE-BY-SIDE CODE & LIVE BROWSER OUTPUT SPLIT VIEW
   ========================================================================== */
/* ==========================================================================
   SIDE-BY-SIDE CODE & LIVE BROWSER OUTPUT SPLIT VIEW
   ========================================================================== */
.code-preview-split {
    display: grid;
    grid-template-columns: minmax(0, 1.15fr) minmax(0, 1fr);
    gap: 20px;
    margin: 28px 0 32px;
    align-items: stretch;
    width: 100%;
    box-sizing: border-box;
}

.code-preview-split .split-col {
    min-width: 0;
    width: 100%;
    border-radius: 14px;
    display: flex;
    flex-direction: column;
    overflow: hidden;
    box-shadow: 0 4px 20px rgba(15, 23, 42, 0.08);
    box-sizing: border-box;
}

/* LEFT COLUMN: DARK IDE CODE BOX */
.code-preview-split .code-col {
    background: #0D1117;
    border: 1.5px solid #30363D;
}

.code-preview-split .code-col .split-header {
    background: #161B22;
    border-bottom: 1.5px solid #30363D;
}

/* RIGHT COLUMN: LIGHT / DARK BROWSER PREVIEW */
.code-preview-split .preview-col {
    background: #FFFFFF !important;
    border: 1.5px solid #CBD5E1 !important;
    width: 100% !important;
    height: auto !important;
    min-height: 200px !important;
    display: flex !important;
    flex-direction: column !important;
}

.code-preview-split .preview-col .split-header {
    background: #F1F5F9;
    border-bottom: 1.5px solid #E2E8F0;
}

.code-preview-split .split-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 16px;
    flex-shrink: 0;
    min-height: 42px;
    box-sizing: border-box;
}

.code-preview-split .split-header-left {
    display: flex;
    align-items: center;
    gap: 10px;
}

.code-preview-split .split-badge {
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.6px;
    padding: 3px 10px;
    border-radius: 9999px;
}

.code-preview-split .code-badge {
    background: rgba(108, 76, 232, 0.25);
    color: #D2A8FF;
    border: 1px solid rgba(192, 132, 252, 0.4);
}

.code-preview-split .preview-badge {
    background: #DEF7EC;
    color: #03543F;
    border: 1px solid #84E1BC;
    font-weight: 700;
}

.code-preview-split .split-file {
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 12px;
    color: #8B949E;
}

.code-preview-split .split-live-dot {
    color: #059669;
    font-size: 12px;
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: 6px;
}

/* CODE AREA & SYNTAX HIGHLIGHTING TOKENS */
.code-preview-split .code-col pre {
    margin: 0 !important;
    padding: 18px !important;
    flex: 1;
    border-radius: 0 !important;
    border: none !important;
    background: #0D1117 !important;
    font-size: 13px !important;
    line-height: 1.65 !important;
    overflow-x: auto !important;
    white-space: pre-wrap !important;
    word-break: break-word !important;
    box-sizing: border-box !important;
}

.code-preview-split .code-col code {
    font-family: 'JetBrains Mono', Consolas, monospace !important;
    font-size: 13px !important;
    line-height: 1.65 !important;
    color: #E6EDF3 !important;
    white-space: pre-wrap !important;
    word-break: break-word !important;
}

/* HTML & JS Code Syntax Highlighting Color Palette (Unified VS Code Dark+ Theme) */
.hl-keyword, .tok-kw, .tok-keyword          { color: #C084FC !important; font-weight: 600 !important; } /* Keywords: const, let, if, for, return, function */
.hl-func, .tok-fn, .tok-method             { color: #FCD34D !important; font-weight: 600 !important; } /* Functions & Methods: querySelectorAll, forEach */
.hl-tag, .tok-tag                          { color: #38BDF8 !important; font-weight: 600 !important; } /* HTML Tags: <div>, <button>, <article> */
.hl-builtin, .tok-sel, .tok-builtin         { color: #38BDF8 !important; font-weight: 600 !important; } /* Built-ins: document, window, console, Array */
.hl-attr, .tok-attr                        { color: #9CDCFE !important; } /* HTML Attributes: class, id, type, href */
.hl-prop, .tok-prop, .tok-property         { color: #7DD3FC !important; } /* Properties: .length, .style, .innerHTML */
.hl-var, .tok-var                          { color: #9CDCFE !important; } /* Variables & Identifiers: textarea, box, header */
.hl-str, .hl-string, .tok-str, .tok-string { color: #FB923C !important; } /* Strings: "text", 'job-card' */
.hl-number, .tok-num, .tok-number, .hl-val, .tok-val { color: #A3E635 !important; font-weight: 600 !important; } /* Numbers & Hex: 0, 2, 0xfc */
.hl-atom, .tok-atom                        { color: #A3E635 !important; font-weight: 600 !important; } /* Atoms: true, false, null, undefined */
.hl-comment, .hl-cmt, .tok-cm, .tok-comment { color: #7EC770 !important; font-style: italic !important; } /* Comments: // comment */
.hl-doctype                                { color: #C084FC !important; font-weight: 700 !important; } /* <!DOCTYPE html> */
.hl-entity                                 { color: #38BDF8 !important; } /* &lt;, &gt;, &amp; */
.hl-op, .tok-op                            { color: #F8FAFC !important; } /* Operators: +, =, <, >>, & */
.hl-punct, .tok-punct, .tok-punc           { color: #F8FAFC !important; } /* Brackets & Punctuation: {}, (), [], ;, , */
.hl-plain                                  { color: #F8FAFC !important; }

/* BROWSER OUTPUT CANVAS */
.code-preview-split .split-output-canvas {
    padding: 20px;
    background: #F1F5F9;
    flex: 1;
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 14px;
    min-height: 180px;
    box-sizing: border-box;
}

/* ELEVATED PREVIEW CARD BOX */
.preview-card-box {
    background: #FFFFFF !important;
    border: 1.5px solid #CBD5E1 !important;
    border-radius: 12px !important;
    padding: 20px !important;
    box-shadow: 0 4px 16px rgba(15, 23, 42, 0.08) !important;
    display: flex !important;
    flex-direction: column !important;
    gap: 12px !important;
    color: #0F172A !important;
    box-sizing: border-box !important;
}

.preview-card-header {
    border-bottom: 1.5px dashed #E2E8F0 !important;
    padding-bottom: 8px !important;
    margin-bottom: 4px !important;
    display: block !important;
}

.preview-card-header h3 {
    margin: 0 0 4px 0 !important;
    color: #6C4CE8 !important;
    font-size: 1.15rem !important;
    font-weight: 800 !important;
}

.preview-card-header time {
    font-size: 12px !important;
    color: #64748B !important;
    display: inline-block !important;
}

.preview-card-footer {
    display: flex !important;
    justify-content: space-between !important;
    align-items: center !important;
    margin-top: 8px !important;
    padding-top: 10px !important;
    border-top: 1px solid #F1F5F9 !important;
    font-size: 13px !important;
    color: #475569 !important;
}

.preview-quote {
    border-left: 3.5px solid #6C4CE8 !important;
    background: #FAF9FF !important;
    padding: 10px 14px !important;
    margin: 0 !important;
    border-radius: 0 8px 8px 0 !important;
    font-style: italic !important;
    color: #1E293B !important;
    font-size: 13.5px !important;
}

.preview-kbd {
    background: #E2E8F0 !important;
    border: 1px solid #94A3B8 !important;
    border-radius: 5px !important;
    padding: 2px 7px !important;
    font-size: 12px !important;
    font-family: 'JetBrains Mono', monospace !important;
    color: #0F172A !important;
    font-weight: 700 !important;
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1) !important;
}

.preview-code {
    background: #F3E8FF !important;
    color: #6C4CE8 !important;
    padding: 2px 7px !important;
    border-radius: 5px !important;
    font-size: 12.5px !important;
    font-family: 'JetBrains Mono', monospace !important;
    font-weight: 600 !important;
    border: 1px solid #E9D5FF !important;
}

.preview-abbr {
    text-decoration: underline dotted #6C4CE8 2px !important;
    cursor: help !important;
    font-weight: 700 !important;
    color: #0F172A !important;
}

.preview-strong {
    color: #6C4CE8 !important;
    font-weight: 800 !important;
}

.split-output-canvas h1, .split-output-canvas h2, .split-output-canvas h3, .split-output-canvas h4 {
    margin: 0 0 6px !important;
    color: #0F172A !important;
    font-weight: 700 !important;
}

.split-output-canvas p {
    margin: 0 0 6px !important;
    font-size: 13.5px !important;
    line-height: 1.55 !important;
    color: #334155 !important;
}

.split-output-canvas section {
    display: block !important;
    margin: 0 !important;
}

.split-output-canvas header, .split-output-canvas footer {
    display: block !important;
}

.split-output-canvas table {
    width: 100%;
    border-collapse: collapse;
    font-size: 13px;
    margin: 0;
    background: #FFFFFF;
    border-radius: 8px;
    overflow: hidden;
}

.split-output-canvas th, .split-output-canvas td {
    padding: 8px 12px;
    border: 1px solid #E2E8F0;
    text-align: left;
}

.split-output-canvas th {
    background: #F1F5F9;
    font-weight: 700;
    color: #0F172A;
}

.split-output-canvas td {
    color: #334155;
}

.split-output-canvas form {
    display: flex;
    flex-direction: column;
    gap: 10px;
    width: 100%;
}

.split-output-canvas label {
    font-size: 12.5px;
    font-weight: 600;
    color: #1E293B;
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.split-output-canvas input, .split-output-canvas select, .split-output-canvas textarea {
    padding: 7px 10px;
    border: 1px solid #CBD5E1;
    border-radius: 6px;
    font-size: 13px;
    background: #FFFFFF;
    color: #0F172A;
    font-family: inherit;
}

.split-output-canvas button, .split-output-canvas .demo-btn {
    padding: 8px 16px;
    background: var(--accent-purple, #6C4CE8);
    color: #FFFFFF;
    border: none;
    border-radius: 6px;
    font-weight: 600;
    font-size: 13px;
    cursor: pointer;
    align-self: flex-start;
}

.split-output-canvas dl {
    display: grid;
    grid-template-columns: max-content 1fr;
    gap: 6px 16px;
    margin: 0;
    font-size: 13.5px;
    background: #FFFFFF;
    padding: 14px;
    border-radius: 8px;
    border: 1px solid #E2E8F0;
}

.split-output-canvas dt {
    font-weight: 700;
    color: var(--accent-purple, #6C4CE8);
}

.split-output-canvas dd {
    margin: 0;
    color: #475569;
}

@media (max-width: 900px) {
    .code-preview-split {
        grid-template-columns: 1fr;
    }
}

/* ==========================================================================
   HANDS-ON PRACTICE & CODE RUNNER SECTION
   ========================================================================== */

.practice-section, .code-editor-container {
    margin-top: 36px;
    padding: 24px;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    box-shadow: 0 4px 16px rgba(23, 32, 51, 0.04);
}

.code-input {
    width: 100%;
    min-height: 130px;
    background: #0D1117;
    border: 1.5px solid #30363D;
    border-radius: var(--radius-sm);
    padding: 14px 16px;
    color: #F0F6FC;
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 13px;
    line-height: 1.55;
    outline: none;
    resize: vertical;
    box-sizing: border-box;
    transition: all 0.2s ease;
    tab-size: 4;
}

.code-input:focus {
    border-color: var(--accent-purple);
    box-shadow: 0 0 0 3px rgba(108, 76, 232, 0.2);
    background: #090D13;
}

.code-input::placeholder {
    color: #6E7681;
}

.editor-actions, .practice-actions {
    display: flex;
    align-items: center;
    gap: 12px;
    margin: 14px 0 10px 0;
    flex-wrap: wrap;
}

.run-button, .run-btn {
    height: 38px;
    min-height: 38px;
    padding: 0 20px;
    border: none;
    border-radius: var(--radius-sm);
    background: var(--accent-purple);
    color: #FFFFFF;
    font-size: 13px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 7px;
    user-select: none;
    line-height: 1;
    text-decoration: none;
    box-sizing: border-box;
    white-space: nowrap;
}

.run-button:hover, .run-btn:hover {
    background: var(--purple-hover);
    box-shadow: 0 4px 14px rgba(108, 76, 232, 0.3);
    transform: translateY(-1.5px);
}

.run-button:active, .run-btn:active {
    transform: translateY(0);
}

.run-button:disabled, .run-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

/* Show / Hide Answer Toggle */
.answer-toggle-btn, .show-answer-btn {
    height: 38px;
    min-height: 38px;
    padding: 0 18px;
    border: 1.5px solid var(--border-color);
    border-radius: var(--radius-sm);
    background: #F8F9FC;
    color: var(--text-secondary);
    font-size: 13px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    user-select: none;
    line-height: 1;
    box-sizing: border-box;
    white-space: nowrap;
}

.answer-toggle-btn:hover, .show-answer-btn:hover {
    border-color: var(--accent-purple);
    color: var(--accent-purple);
    background: var(--purple-light);
    transform: translateY(-1.5px);
    box-shadow: 0 2px 8px rgba(108, 76, 232, 0.12);
}

.answer-toggle-btn:active, .show-answer-btn:active {
    transform: translateY(0);
}

.answer-toggle-btn.revealed, .show-answer-btn.revealed {
    border-color: #F97316;
    color: #F97316;
    background: rgba(249, 115, 22, 0.08);
}

/* Terminal Console Output Box */
.output-box, #domOutput {
    margin-top: 14px;
    background: #0B1120;
    border: 1.5px solid #1E293B;
    border-radius: var(--radius-sm);
    padding: 12px 16px;
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 12.5px;
    line-height: 1.5;
    color: #94A3B8;
    min-height: 44px;
    white-space: pre-wrap;
    word-break: break-word;
    box-sizing: border-box;
    transition: all 0.2s ease;
}

.output-title {
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.8px;
    color: #64748B;
    margin-bottom: 6px;
    display: flex;
    align-items: center;
    gap: 6px;
}

.output-content {
    color: #4ADE80;
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 12.5px;
    white-space: pre-wrap;
}

/* Model Answer Panel */
.answer-panel {
    display: none;
    margin-top: 14px;
    border: 1.5px solid rgba(249, 115, 22, 0.35);
    border-left: 4px solid #F97316;
    border-radius: var(--radius-sm);
    overflow: hidden;
    animation: fadeInSlide 0.25s ease-out;
}

.answer-panel.visible {
    display: block;
}

.answer-panel-header {
    display: flex;
    align-items: center;
    gap: 8px;
    background: rgba(249, 115, 22, 0.1);
    padding: 8px 14px;
    font-size: 11.5px;
    font-weight: 700;
    color: #F97316;
    letter-spacing: 0.06em;
    text-transform: uppercase;
}

.answer-panel pre {
    margin: 0;
    padding: 14px 16px;
    background: #0D1117;
    color: #F0F6FC;
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 12.5px;
    line-height: 1.55;
    white-space: pre-wrap;
    word-break: break-word;
    overflow-x: auto;
}

/* ==========================================================================
   EXAMPLE CODE OUTPUT PREVIEWS (COMPACT & ON-DEMAND COLLAPSIBLE)
   ========================================================================== */
.example-output-box {
    margin: 0 0 20px 0;
    background: #0D1117;
    border: 1px solid #21262D;
    border-top: none;
    border-bottom-left-radius: var(--radius-md);
    border-bottom-right-radius: var(--radius-md);
    overflow: hidden;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
    transition: border-color 0.2s ease;
}

.code-snippet-container + .example-output-box,
pre + .example-output-box {
    margin-top: -14px;
}

.example-output-box .example-output-header {
    display: flex;
    align-items: center;
    justify-content: flex-start;
    gap: 12px;
    padding: 7px 14px;
    background: #161B22;
    cursor: pointer;
    user-select: none;
    transition: background 0.15s ease;
    border-bottom: 1px solid transparent;
}

.example-output-box:hover .example-output-header {
    background: #1C2128;
}

.example-output-box.is-open .example-output-header {
    border-bottom-color: #21262D;
}

.example-output-box .example-output-header::before {
    display: none !important;
    content: none !important;
}

.example-output-box .terminal-dots {
    display: inline-flex;
    gap: 5px;
    align-items: center;
}

.example-output-box .terminal-dots .dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    display: inline-block;
}

.example-output-box .terminal-dots .dot.red { background: #FF5F56; }
.example-output-box .terminal-dots .dot.yellow { background: #FFBD2E; }
.example-output-box .terminal-dots .dot.green { background: #27C93F; }

.example-output-box .output-label {
    color: #8B949E;
    font-size: 11px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    font-family: 'JetBrains Mono', Consolas, monospace;
    display: inline-flex;
    align-items: center;
}

.example-output-box .toggle-output-btn {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    background: linear-gradient(135deg, #6C4CE8 0%, #5333D6 100%);
    color: #FFFFFF;
    border: 1px solid #7C5EF8;
    border-radius: 6px;
    padding: 4px 12px;
    font-size: 11.5px;
    font-weight: 700;
    font-family: 'Inter', -apple-system, sans-serif;
    letter-spacing: 0.03em;
    cursor: pointer;
    box-shadow: 0 2px 6px rgba(108, 76, 232, 0.35);
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    margin-left: 0;
}

.example-output-box .toggle-output-btn:hover {
    background: linear-gradient(135deg, #7C5EF8 0%, #6C4CE8 100%);
    box-shadow: 0 4px 10px rgba(108, 76, 232, 0.5);
    transform: translateY(-1px);
    color: #FFFFFF;
}

.example-output-box .toggle-output-btn .chevron-icon {
    transition: transform 0.25s ease;
}

.example-output-box.is-open .toggle-output-btn .chevron-icon {
    transform: rotate(180deg);
}

.example-output-box.is-open .toggle-output-btn {
    background: #1A2234;
    color: #C4B5FD;
    border-color: #6C4CE8;
    box-shadow: 0 0 0 2px rgba(108, 76, 232, 0.25);
    transform: none;
}

/* Collapsible Content Area */
.example-output-box .example-output-content {
    display: none;
    padding: 12px 16px;
    color: #58A6FF;
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 12px;
    line-height: 1.5;
    white-space: pre-wrap;
    word-break: break-word;
    background: #090D13;
}

.example-output-box.is-open .example-output-content {
    display: block;
    animation: fadeInOutput 0.2s ease forwards;
}

@keyframes fadeInOutput {
    from {
        opacity: 0;
        transform: translateY(-4px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.example-output-box .example-output-content.rendered-ui {
    background: #F8FAFC;
    color: #1F2937;
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    padding: 14px 18px;
    border-top: 1px solid #E2E8F0;
}

.example-output-box .example-output-content.rendered-ui .ui-preview-card {
    background: #FFFFFF;
    border: 1px solid #E2E8F0;
    border-radius: 8px;
    padding: 12px 16px;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
}

/* ==========================================================================
   TWO-STAGE PRACTICE CHALLENGE WORKSPACE
   ========================================================================== */
.challenge-card {
    margin: 28px 0;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    box-shadow: 0 4px 18px rgba(23, 32, 51, 0.05);
    overflow: hidden;
    transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

.challenge-card:hover {
    border-color: rgba(108, 76, 232, 0.3);
    box-shadow: 0 8px 24px rgba(108, 76, 232, 0.08);
}

.challenge-header {
    padding: 24px;
    background: #FFFFFF;
}

.challenge-badge-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 12px;
    flex-wrap: wrap;
    gap: 8px;
}

.challenge-badge {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 4px 12px;
    background: var(--purple-light);
    color: var(--accent-purple);
    border: 1px solid rgba(108, 76, 232, 0.15);
    border-radius: 999px;
    font-size: 12px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.challenge-tag {
    font-size: 11.5px;
    font-weight: 600;
    color: var(--text-secondary);
    background: #F1F5F9;
    padding: 3px 10px;
    border-radius: 6px;
}

.challenge-title {
    font-size: 17px;
    font-weight: 700;
    color: var(--text-primary);
    margin: 0 0 10px 0;
}

.challenge-desc {
    font-size: 14px;
    color: #4B5563;
    line-height: 1.6;
    margin: 0 0 14px 0;
}

.challenge-task-summary {
    background: #F8FAFC;
    border: 1px solid #E2E8F0;
    border-left: 3.5px solid var(--accent-purple);
    border-radius: var(--radius-sm);
    padding: 12px 16px;
    margin: 12px 0;
    font-size: 13.5px;
}

.challenge-task-summary strong {
    color: #1E293B;
    display: block;
    margin-bottom: 6px;
}

.challenge-task-summary ul {
    margin: 0;
    padding-left: 18px;
    color: #475569;
}

.challenge-task-summary li {
    margin-bottom: 4px;
}

.challenge-expected {
    margin: 12px 0 16px 0;
    font-size: 13px;
    color: #4B5563;
    display: flex;
    align-items: flex-start;
    gap: 8px;
    flex-wrap: wrap;
}

.expected-badge {
    font-weight: 700;
    color: #059669;
    background: #ECFDF5;
    padding: 2px 8px;
    border-radius: 4px;
    border: 1px solid rgba(16, 185, 129, 0.2);
    font-size: 11.5px;
    white-space: nowrap;
}

.challenge-expected code {
    background: #F1F5F9;
    color: #0F172A;
    padding: 2px 6px;
    border-radius: 4px;
    font-family: 'JetBrains Mono', Consolas, monospace;
    font-size: 12.5px;
}

.challenge-actions-bar {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-top: 16px;
}

.start-solve-btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 22px;
    background: var(--accent-purple);
    color: #FFFFFF;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 13.5px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
    box-shadow: 0 2px 8px rgba(108, 76, 232, 0.2);
}

.start-solve-btn:hover {
    background: var(--purple-hover);
    transform: translateY(-1.5px);
    box-shadow: 0 4px 14px rgba(108, 76, 232, 0.3);
}

.start-solve-btn .chevron-icon {
    transition: transform 0.2s ease;
}

.start-solve-btn.is-active .chevron-icon {
    transform: rotate(180deg);
}

/* Collapsible Workspace */
.challenge-workspace {
    display: none;
    padding: 20px 24px 24px 24px;
    background: #F8FAFC;
    border-top: 1px solid #E2E8F0;
    animation: slideDownFade 0.25s cubic-bezier(0.16, 1, 0.3, 1);
}

.challenge-workspace.is-expanded {
    display: block;
}

@keyframes slideDownFade {
    from {
        opacity: 0;
        transform: translateY(-8px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.workspace-guide {
    display: flex;
    align-items: flex-start;
    gap: 10px;
    padding: 10px 14px;
    background: #EFF6FF;
    border: 1px solid #BFDBFE;
    border-radius: var(--radius-sm);
    margin-bottom: 14px;
    font-size: 13px;
    color: #1E40AF;
}

.code-editor-topbar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    background: #161B22;
    padding: 8px 14px;
    border-top-left-radius: var(--radius-sm);
    border-top-right-radius: var(--radius-sm);
    border-bottom: 1px solid #30363D;
}

.editor-tab {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    color: #C9D1D9;
    font-size: 12px;
    font-weight: 600;
    font-family: 'JetBrains Mono', Consolas, monospace;
}

.tab-dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: #6C4CE8;
}

.reset-code-btn {
    background: transparent;
    border: 1px solid #30363D;
    color: #8B949E;
    font-size: 11.5px;
    font-weight: 600;
    padding: 3px 10px;
    border-radius: 4px;
    cursor: pointer;
    transition: all 0.15s ease;
    display: inline-flex;
    align-items: center;
    gap: 5px;
}

.reset-code-btn:hover {
    background: #21262D;
    color: #F0F6FC;
    border-color: #8B949E;
}

.challenge-workspace .code-input {
    border-top-left-radius: 0;
    border-top-right-radius: 0;
    min-height: 140px;
}


.chapter-bottom-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    margin-top: 48px;
    padding-top: 24px;
    border-top: 1px solid var(--border-color);
    flex-wrap: wrap;
}

.chapter-nav-btn {
    text-decoration: none;
    color: var(--text-primary);
    font-size: 13.5px;
    font-weight: 600;
    padding: 10px 18px;
    background: #FFFFFF;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    transition: all 0.15s ease;
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

.chapter-nav-btn:hover {
    border-color: var(--accent-purple);
    color: var(--accent-purple);
    background: var(--purple-light);
}

.chapter-nav-btn.home-btn {
    background: var(--purple-light);
    color: var(--accent-purple);
    border-color: rgba(108, 76, 232, 0.2);
}

/* ==========================================================================
   MULTI-DEVICE RESPONSIVE LAYOUT (Mobile, Tablet, Laptop, Desktop, 4K)
   ========================================================================== */

/* 1. Large Laptops & Small Desktops (1025px - 1280px) */
@media (max-width: 1280px) {
    .lesson-page {
        padding: 28px 24px 80px 280px;
    }
    .page-index-sidebar {
        width: 240px;
        left: 20px;
    }
}

/* 2. Tablets & Medium Screens (769px - 1024px) */
@media (max-width: 1024px) {
    .lesson-page {
        padding: 24px 16px 80px 252px;
    }
    .page-index-sidebar {
        width: 220px;
        left: 16px;
        padding: 16px 12px;
    }
}

/* 3. Mobile & Portrait Tablets (<= 768px) */
@media (max-width: 768px) {
    .lesson-page {
        padding: 16px 12px 60px 12px;
        max-width: 100%;
    }
    .page-index-sidebar {
        position: static !important;
        top: 0 !important;
        left: 0 !important;
        width: 100%;
        max-height: none;
        margin-bottom: 20px;
        border-radius: var(--radius-md);
    }
    .chapter-hero-banner {
        flex-direction: column;
        align-items: flex-start;
        gap: 16px;
        padding: 24px 18px;
    }
    .chapter-hero-title {
        font-size: 28px;
    }
    .chapter-hero-icon-art {
        display: none;
    }
    .chapter-hero-banner.is-sticky {
        position: sticky;
        top: 56px;
        width: 100%;
        max-width: 100%;
        height: 48px;
        min-height: 48px;
        padding: 0 14px;
        margin-bottom: 16px;
        border-radius: 0 0 var(--radius-sm) var(--radius-sm);
        z-index: 1050;
    }
    .chapter-hero-banner.is-sticky .chapter-hero-content {
        display: flex;
        align-items: center;
        justify-content: space-between;
        width: 100%;
        gap: 8px;
    }
    .chapter-hero-banner.is-sticky .chapter-hero-tag {
        font-size: 11px;
        padding: 2.5px 8px;
    }
    .chapter-hero-banner.is-sticky .chapter-hero-title {
        font-size: 13.5px;
    }
    .concept-cards-grid {
        grid-template-columns: 1fr !important;
        gap: 14px;
    }
    .dom-playground {
        grid-template-columns: 1fr;
        gap: 16px;
    }
    .cheat-sheet {
        grid-template-columns: 1fr;
        gap: 10px;
    }
    .chapter-top-nav {
        display: flex;
        flex-direction: column;
        align-items: stretch;
        gap: 12px;
        margin-bottom: 20px;
        padding-bottom: 16px;
    }
    .top-nav-meta {
        display: flex;
        align-items: center;
        justify-content: space-between;
        width: 100%;
        gap: 8px;
    }
    .top-nav-meta .back-to-js-link {
        font-size: 12.5px;
        padding: 5px 12px;
    }
    .top-nav-meta .chapter-badge {
        font-size: 12px;
        padding: 4px 10px;
        margin: 0;
        white-space: nowrap;
    }
    .top-nav-actions {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 8px;
        width: 100%;
    }
    .top-nav-actions .top-nav-btn {
        width: 100%;
        justify-content: center;
        padding: 8px 10px;
        font-size: 13px;
        text-align: center;
        box-sizing: border-box;
    }
    .lesson-card {
        padding: 24px 16px;
    }
    .chapter-bottom-nav {
        flex-direction: column;
        align-items: stretch;
        gap: 10px;
    }
    .chapter-nav-btn {
        justify-content: center;
    }
}

/* 4. Small Mobile Screens (<= 480px) */
@media (max-width: 480px) {
    .chapter-hero-banner.is-sticky {
        padding: 0 10px;
    }
    .chapter-hero-banner.is-sticky .chapter-hero-tag {
        font-size: 10.5px;
        padding: 2px 6px;
    }
    .chapter-hero-banner.is-sticky .chapter-hero-title {
        font-size: 12.5px;
        max-width: 160px;
    }
    .lesson-card h2 {
        font-size: 22px;
    }
    .lesson-card h3 {
        font-size: 18px;
    }
}