/* ============================================
   Foundations of AI - Premium Learning Platform
   ============================================ */

/* CSS Variables - Design System */
:root {
    /* Color Palette - Sophisticated Dark Theme (Default) */
    --bg-primary: #0d0f12;
    --bg-secondary: #13161b;
    --bg-tertiary: #1a1e25;
    --bg-elevated: #21262e;
    --bg-hover: #282e38;

    --surface-1: #1e2229;
    --surface-2: #252a33;
    --surface-3: #2d333d;

    --text-primary: #e8eaed;
    --text-secondary: #9aa0a9;
    --text-tertiary: #6b7280;
    --text-muted: #4b5563;

    /* Accent Colors */
    --accent-gold: #d4a855;
    --accent-gold-dim: #a68642;
    --accent-gold-glow: rgba(212, 168, 85, 0.15);

    --accent-blue: #5b9bd5;
    --accent-blue-dim: #4a7fb0;

    --accent-emerald: #50b892;
    --accent-coral: #e07a5f;
    --accent-violet: #9d7cd8;

    /* Semantic Colors */
    --success: #4ade80;
    --success-bg: rgba(74, 222, 128, 0.1);
    --error: #f87171;
    --error-bg: rgba(248, 113, 113, 0.1);
    --warning: #fbbf24;
    --info: #60a5fa;

    /* Class Colors for Lab */
    --class-a: #e07a5f;
    --class-b: #5b9bd5;

    /* Typography */
    --font-display: 'Crimson Pro', Georgia, serif;
    --font-body: 'DM Sans', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

    /* Spacing Scale */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;
    --space-2xl: 3rem;
    --space-3xl: 4rem;

    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;

    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 20px rgba(212, 168, 85, 0.2);

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 400ms ease;

    /* Layout */
    --sidebar-width: 300px;
    --content-max-width: 780px;

    /* Header Height for Mobile */
    --header-height: 60px;
}

/* Light Theme */
[data-theme="light"] {
    --bg-primary: #f8f9fa;
    --bg-secondary: #ffffff;
    --bg-tertiary: #f1f3f5;
    --bg-elevated: #ffffff;
    --bg-hover: #e9ecef;

    --surface-1: #ffffff;
    --surface-2: #e9ecef;
    --surface-3: #dee2e6;

    --text-primary: #1a1a2e;
    --text-secondary: #495057;
    --text-tertiary: #6c757d;
    --text-muted: #adb5bd;

    --accent-gold: #b8860b;
    --accent-gold-dim: #8b6914;
    --accent-gold-glow: rgba(184, 134, 11, 0.12);

    --accent-blue: #2563eb;
    --accent-blue-dim: #1d4ed8;

    --accent-emerald: #059669;
    --accent-coral: #dc2626;
    --accent-violet: #7c3aed;

    --success: #16a34a;
    --success-bg: rgba(22, 163, 74, 0.1);
    --error: #dc2626;
    --error-bg: rgba(220, 38, 38, 0.1);
    --warning: #d97706;
    --info: #2563eb;

    --class-a: #dc2626;
    --class-b: #2563eb;

    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.15);
    --shadow-glow: 0 0 20px rgba(184, 134, 11, 0.15);
}

/* Reset & Base */
*,
*::before,
*::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-body);
    font-size: 1rem;
    line-height: 1.7;
    color: var(--text-primary);
    background: var(--bg-primary);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    transition: background-color var(--transition-base), color var(--transition-base);
}

/* Smooth theme transitions for key elements */
.sidebar,
.main-content,
.content-header,
.mobile-header,
.lab-container,
.quiz-container,
.definition-block,
.layer,
.concept-card {
    transition: background-color var(--transition-base),
        border-color var(--transition-base),
        color var(--transition-base);
}

/* App Container */
.app-container {
    display: flex;
    min-height: 100vh;
}

/* ============================================
   Mobile Header & Hamburger Menu
   ============================================ */
.mobile-header {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--header-height);
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--surface-2);
    z-index: 200;
    padding: 0 var(--space-md);
    align-items: center;
    justify-content: space-between;
}

.mobile-logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    text-decoration: none;
}

.mobile-logo .logo-icon {
    font-size: 1.25rem;
    color: var(--accent-gold);
}

.mobile-logo .logo-text {
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.mobile-actions {
    display: flex;
    align-items: center;
    gap: var(--space-xs);
}

/* Hamburger Button */
.hamburger-btn {
    display: none;
    width: 44px;
    height: 44px;
    padding: 0;
    background: transparent;
    border: none;
    cursor: pointer;
    position: relative;
    z-index: 250;
}

.hamburger-icon {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    width: 100%;
    height: 100%;
}

.hamburger-icon span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 1px;
    transition: all var(--transition-fast);
    position: relative;
}

.hamburger-icon span:nth-child(1) {
    transform: translateY(-6px);
}

.hamburger-icon span:nth-child(3) {
    transform: translateY(6px);
}

/* Hamburger Animation */
.hamburger-btn.active .hamburger-icon span:nth-child(1) {
    transform: translateY(0) rotate(45deg);
}

.hamburger-btn.active .hamburger-icon span:nth-child(2) {
    opacity: 0;
    transform: scaleX(0);
}

.hamburger-btn.active .hamburger-icon span:nth-child(3) {
    transform: translateY(0) rotate(-45deg);
}

/* Theme Toggle Button */
.theme-toggle {
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--surface-2);
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-size: 1.1rem;
}

.theme-toggle:hover {
    background: var(--surface-3);
    color: var(--text-primary);
}

.theme-toggle .sun-icon {
    display: none;
}

.theme-toggle .moon-icon {
    display: block;
}

[data-theme="light"] .theme-toggle .sun-icon {
    display: block;
}

[data-theme="light"] .theme-toggle .moon-icon {
    display: none;
}

/* Sidebar Overlay (Mobile) */
.sidebar-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 150;
    opacity: 0;
    transition: opacity var(--transition-base);
}

.sidebar-overlay.active {
    opacity: 1;
}

/* ============================================
   Sidebar Navigation
   ============================================ */
.sidebar {
    width: var(--sidebar-width);
    min-width: var(--sidebar-width);
    background: var(--bg-secondary);
    border-right: 1px solid var(--surface-2);
    display: flex;
    flex-direction: column;
    position: fixed;
    height: 100vh;
    overflow-y: auto;
    z-index: 200;
    transition: transform var(--transition-base);
}

.sidebar-header {
    padding: var(--space-xl);
    border-bottom: 1px solid var(--surface-2);
}

.logo {
    display: flex;
    align-items: flex-start;
    gap: var(--space-md);
    text-decoration: none;
    color: inherit;
    transition: opacity var(--transition-fast);
}

.logo:hover {
    opacity: 0.85;
}

.logo-icon {
    font-size: 1.75rem;
    color: var(--accent-gold);
    line-height: 1;
    margin-top: 2px;
}

.logo-img {
    width: 28px;
    height: 28px;
    object-fit: contain;
    flex-shrink: 0;
}


.logo-text {
    font-family: var(--font-display);
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
    line-height: 1.2;
    letter-spacing: -0.01em;
}

.logo-subtext {
    display: block;
    font-family: var(--font-body);
    font-size: 0.75rem;
    font-weight: 400;
    color: var(--text-secondary);
    letter-spacing: 0.03em;
    margin-top: 0.15rem;
    text-decoration: none;
}

.curriculum-nav {
    flex: 1;
    padding: var(--space-lg) 0;
    overflow-y: auto;
}

.nav-section {
    margin-bottom: var(--space-xl);
}

.nav-section-title {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--text-tertiary);
    padding: 0 var(--space-xl);
    margin-bottom: var(--space-sm);
}

.nav-list {
    list-style: none;
}

.nav-item {
    display: flex;
    align-items: baseline;
    gap: var(--space-md);
    padding: var(--space-sm) var(--space-xl);
    cursor: pointer;
    transition: all var(--transition-fast);
    border-left: 2px solid transparent;
}

.nav-item:hover {
    background: var(--bg-hover);
}

.nav-item.active {
    background: var(--accent-gold-glow);
    border-left-color: var(--accent-gold);
}

.nav-item.active .nav-label {
    color: var(--text-primary);
}

.nav-item.active .nav-number {
    color: var(--accent-gold);
}

.nav-number {
    font-family: var(--font-mono);
    font-size: 0.75rem;
    color: var(--text-muted);
    min-width: 2rem;
}

.nav-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.4;
}

.sidebar-footer {
    padding: var(--space-lg) var(--space-xl);
    border-top: 1px solid var(--surface-2);
}

.progress-bar {
    height: 4px;
    background: var(--surface-3);
    border-radius: 2px;
    overflow: hidden;
    margin-bottom: var(--space-sm);
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-gold-dim), var(--accent-gold));
    border-radius: 2px;
    transition: width var(--transition-slow);
}

.progress-text {
    font-size: 0.75rem;
    color: var(--text-tertiary);
}

/* Sidebar Theme Toggle */
.sidebar-theme-toggle {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: var(--space-md);
    padding-top: var(--space-md);
    border-top: 1px solid var(--surface-2);
}

.sidebar-theme-toggle span {
    font-size: 0.75rem;
    color: var(--text-tertiary);
}

.sidebar-theme-toggle .theme-toggle {
    width: 36px;
    height: 36px;
    font-size: 1rem;
}

/* ============================================
   Collapsible Sidebar Toggle
   ============================================ */

/* Sidebar Toggle Button - Inside sidebar header */
.sidebar-toggle {
    position: absolute;
    top: 50%;
    right: 12px;
    transform: translateY(-50%);
    width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--surface-2);
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    cursor: pointer;
    z-index: 10;
    transition: all var(--transition-fast);
}

.sidebar-toggle:hover {
    background: var(--surface-3);
    color: var(--text-primary);
}

.sidebar-toggle svg {
    width: 16px;
    height: 16px;
    transition: transform var(--transition-fast);
}

/* Make sidebar header relative for toggle positioning */
.sidebar-header {
    position: relative;
}

/* Floating toggle when sidebar is collapsed */
.sidebar-toggle-floating {
    position: fixed;
    top: 16px;
    left: 16px;
    width: 44px;
    height: 44px;
    display: none;
    align-items: center;
    justify-content: center;
    background: var(--bg-elevated);
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    cursor: pointer;
    z-index: 9999;
    transition: all var(--transition-fast);
    box-shadow: var(--shadow-md);
    pointer-events: auto;
    -webkit-tap-highlight-color: transparent;
}

.sidebar-toggle-floating:hover {
    background: var(--surface-2);
    color: var(--text-primary);
}

.sidebar-toggle-floating svg {
    width: 20px;
    height: 20px;
}

/* Sidebar collapsed state */
body.sidebar-collapsed .sidebar {
    transform: translateX(-100%);
}

body.sidebar-collapsed .main-content {
    margin-left: 0;
}

body.sidebar-collapsed .content-header {
    padding-left: 72px;
}

/* Show floating toggle when sidebar is collapsed */
body.sidebar-collapsed .sidebar-toggle-floating {
    display: flex;
}

/* Hide in-sidebar toggle when collapsed (it's off-screen anyway) */
body.sidebar-collapsed .sidebar-toggle {
    opacity: 0;
}

/* Sidebar backdrop/overlay - shown on mobile and when sidebar overlays content */
.sidebar-backdrop {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0);
    z-index: 190;
    pointer-events: none;
    transition: background var(--transition-base);
}

body:not(.sidebar-collapsed) .sidebar-backdrop.active {
    background: rgba(0, 0, 0, 0.4);
    pointer-events: auto;
}

/* Smooth transitions */
.sidebar,
.main-content,
.content-header {
    transition: all 280ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* Desktop: sidebar push content */
@media (min-width: 1025px) {
    body:not(.sidebar-collapsed) .sidebar-backdrop {
        display: none;
    }
}

/* Tablet and below: sidebar overlays content */
@media (max-width: 1024px) {

    /* Floating toggle positioning for mobile */
    .sidebar-toggle-floating {
        top: 12px;
        left: 12px;
    }

    /* Ensure floating toggle is always visible when sidebar collapsed on mobile */
    body.sidebar-collapsed .sidebar-toggle-floating {
        display: flex !important;
    }

    body.sidebar-collapsed .content-header {
        padding-left: 60px;
    }

    /* Sidebar overlays instead of pushing */
    .sidebar {
        position: fixed;
        box-shadow: var(--shadow-lg);
    }

    .main-content {
        margin-left: 0 !important;
    }

    body:not(.sidebar-collapsed) .sidebar-backdrop.active {
        background: rgba(0, 0, 0, 0.5);
    }
}

/* Very small screens */
@media (max-width: 480px) {
    .sidebar {
        width: 100%;
        max-width: 320px;
    }
}

/* ============================================
   Main Content Area
   ============================================ */
.main-content {
    flex: 1;
    margin-left: var(--sidebar-width);
    background: var(--bg-primary);
    min-height: 100vh;
}

.content-header {
    position: sticky;
    top: 0;
    z-index: 50;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--space-md) var(--space-2xl);
    background: rgba(13, 15, 18, 0.85);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--surface-2);
}

.breadcrumb {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 0.875rem;
    color: var(--text-tertiary);
}

.breadcrumb-sep {
    color: var(--text-muted);
}

.header-actions {
    display: flex;
    gap: var(--space-sm);
}

.btn-icon {
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: transparent;
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-icon:hover {
    background: var(--surface-2);
    color: var(--text-primary);
}

/* ============================================
   Module Content
   ============================================ */
.module-content {
    max-width: var(--content-max-width);
    margin: 0 auto;
    padding: var(--space-3xl) var(--space-2xl);
}

/* Module Hero */
.module-hero {
    margin-bottom: var(--space-3xl);
    padding-bottom: var(--space-2xl);
    border-bottom: 1px solid var(--surface-2);
}

.module-meta {
    display: flex;
    gap: var(--space-md);
    margin-bottom: var(--space-lg);
}

.module-tag {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--accent-gold);
    background: var(--accent-gold-glow);
    padding: var(--space-xs) var(--space-md);
    border-radius: var(--radius-sm);
}

.module-duration {
    font-size: 0.8rem;
    color: var(--text-tertiary);
}

.module-title {
    font-family: var(--font-display);
    font-size: 2.75rem;
    font-weight: 600;
    color: var(--text-primary);
    line-height: 1.15;
    margin-bottom: var(--space-lg);
    letter-spacing: -0.02em;
}

.module-subtitle {
    font-size: 1.125rem;
    color: var(--text-secondary);
    line-height: 1.7;
    max-width: 600px;
}

/* Learning Objectives */
.learning-objectives {
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-3xl);
}

.section-label {
    font-family: var(--font-mono);
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--accent-blue);
    margin-bottom: var(--space-md);
}

.objectives-list {
    list-style: none;
}

.objectives-list li {
    position: relative;
    padding-left: var(--space-xl);
    margin-bottom: var(--space-sm);
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.objectives-list li::before {
    content: '◇';
    position: absolute;
    left: 0;
    color: var(--accent-gold-dim);
    font-size: 0.75rem;
}

.objectives-list li:last-child {
    margin-bottom: 0;
}

/* Content Sections */
.content-section {
    margin-bottom: var(--space-3xl);
}

.section-heading {
    font-family: var(--font-display);
    font-size: 1.75rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-xl);
    padding-bottom: var(--space-md);
    border-bottom: 1px solid var(--surface-2);
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.lab-icon,
.quiz-icon {
    color: var(--accent-gold);
}

/* Definition Block */
.definition-block {
    background: linear-gradient(135deg, var(--surface-1), var(--surface-2));
    border-left: 3px solid var(--accent-gold);
    border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
    padding: var(--space-xl);
    margin-bottom: var(--space-xl);
}

.definition-marker {
    font-family: var(--font-mono);
    font-size: 0.65rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.1em;
    color: var(--accent-gold);
    margin-bottom: var(--space-sm);
}

.definition-text {
    font-family: var(--font-display);
    font-size: 1.15rem;
    line-height: 1.7;
    color: var(--text-primary);
}

.definition-text em {
    color: var(--accent-gold);
    font-style: italic;
}

/* Explanation Layers */
.explanation-layers {
    display: flex;
    flex-direction: column;
    gap: var(--space-lg);
}

.layer {
    background: var(--surface-1);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    border: 1px solid var(--surface-2);
    transition: border-color var(--transition-base);
}

.layer:hover {
    border-color: var(--surface-3);
}

.layer-badge {
    display: inline-block;
    font-family: var(--font-mono);
    font-size: 0.65rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    padding: var(--space-xs) var(--space-sm);
    border-radius: var(--radius-sm);
    margin-bottom: var(--space-md);
}

.layer-intuition .layer-badge {
    background: rgba(80, 184, 146, 0.15);
    color: var(--accent-emerald);
}

.layer-technical .layer-badge {
    background: rgba(91, 155, 213, 0.15);
    color: var(--accent-blue);
}

.layer-practical .layer-badge {
    background: rgba(157, 124, 216, 0.15);
    color: var(--accent-violet);
}

.layer p {
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.layer p:last-child {
    margin-bottom: 0;
}

.layer em {
    color: var(--text-primary);
    font-style: italic;
}

.technical-list {
    margin: var(--space-md) 0;
    padding-left: var(--space-xl);
}

.technical-list li {
    margin-bottom: var(--space-md);
    color: var(--text-secondary);
}

.technical-list li:last-child {
    margin-bottom: 0;
}

.technical-list strong {
    color: var(--text-primary);
}

/* Taxonomy Visual */
.taxonomy-visual {
    display: flex;
    justify-content: center;
    padding: var(--space-2xl) 0;
    margin-bottom: var(--space-xl);
}

.taxonomy-ring {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    text-align: center;
    padding: var(--space-xl);
}

.ring-ai {
    width: 420px;
    height: 420px;
    background: linear-gradient(145deg, rgba(212, 168, 85, 0.08), rgba(212, 168, 85, 0.03));
    border: 2px solid rgba(212, 168, 85, 0.3);
}

.ring-ml {
    width: 300px;
    height: 300px;
    background: linear-gradient(145deg, rgba(91, 155, 213, 0.1), rgba(91, 155, 213, 0.05));
    border: 2px solid rgba(91, 155, 213, 0.3);
}

.ring-dl {
    width: 160px;
    height: 160px;
    background: linear-gradient(145deg, rgba(80, 184, 146, 0.12), rgba(80, 184, 146, 0.06));
    border: 2px solid rgba(80, 184, 146, 0.4);
}

.ring-label {
    font-family: var(--font-display);
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-xs);
}

.ring-description {
    font-size: 0.7rem;
    color: var(--text-tertiary);
    max-width: 140px;
    line-height: 1.4;
}

.ring-dl .ring-label {
    font-size: 0.8rem;
}

.ring-dl .ring-description {
    font-size: 0.6rem;
    max-width: 120px;
}

/* Concept Card */
.concept-card {
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-lg);
}

.concept-title {
    font-family: var(--font-display);
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-md);
}

.concept-card p {
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.concept-card p:last-child {
    margin-bottom: 0;
}

.formal-quote {
    background: var(--bg-tertiary);
    border-left: 3px solid var(--accent-blue-dim);
    padding: var(--space-lg);
    margin: var(--space-lg) 0;
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
    font-family: var(--font-display);
    font-style: italic;
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.7;
}

/* Lead Paragraph */
.lead-paragraph {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-xl);
    line-height: 1.8;
}

/* Key Insight */
.key-insight {
    display: flex;
    gap: var(--space-lg);
    background: linear-gradient(135deg, var(--accent-gold-glow), transparent);
    border: 1px solid rgba(212, 168, 85, 0.2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin: var(--space-xl) 0;
}

.insight-icon {
    font-size: 1.5rem;
    color: var(--accent-gold);
    flex-shrink: 0;
}

.insight-content h4 {
    font-family: var(--font-display);
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-sm);
}

.insight-content p {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

/* Comparison Table */
.comparison-table {
    margin: var(--space-xl) 0;
}

.table-title {
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-md);
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.9rem;
}

thead {
    background: var(--surface-2);
}

th {
    text-align: left;
    padding: var(--space-md);
    font-weight: 600;
    color: var(--text-primary);
    border-bottom: 1px solid var(--surface-3);
}

td {
    padding: var(--space-md);
    color: var(--text-secondary);
    border-bottom: 1px solid var(--surface-2);
}

tr:hover td {
    background: var(--surface-1);
}

/* Misconception Cards */
.misconception-card {
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-lg);
}

.misconception-header {
    display: flex;
    align-items: flex-start;
    gap: var(--space-md);
    margin-bottom: var(--space-md);
}

.misconception-icon {
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--error-bg);
    color: var(--error);
    border-radius: 50%;
    font-size: 0.75rem;
    font-weight: 700;
    flex-shrink: 0;
}

.misconception-claim {
    font-family: var(--font-display);
    font-size: 1.1rem;
    font-weight: 500;
    color: var(--text-primary);
    font-style: italic;
}

.misconception-body {
    padding-left: calc(24px + var(--space-md));
}

.misconception-problem {
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
    font-size: 0.95rem;
}

.misconception-correction {
    background: var(--success-bg);
    border-radius: var(--radius-md);
    padding: var(--space-md);
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.misconception-correction strong {
    color: var(--success);
}

/* ============================================
   Interactive Lab
   ============================================ */
.lab-section {
    background: var(--bg-secondary);
    margin-left: calc(-1 * var(--space-2xl));
    margin-right: calc(-1 * var(--space-2xl));
    padding: var(--space-2xl);
    border-radius: var(--radius-xl);
}

.lab-introduction {
    margin-bottom: var(--space-xl);
}

.lab-introduction p {
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.lab-introduction p:last-child {
    margin-bottom: 0;
}

.lab-container {
    background: var(--bg-tertiary);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
}

.lab-controls {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-xl);
    margin-bottom: var(--space-xl);
    padding-bottom: var(--space-xl);
    border-bottom: 1px solid var(--surface-2);
}

.control-group {
    flex: 1;
    min-width: 200px;
}

.control-label {
    display: block;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-tertiary);
    margin-bottom: var(--space-sm);
}

.class-selector {
    display: flex;
    gap: var(--space-sm);
}

.class-btn {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    padding: var(--space-sm) var(--space-md);
    background: var(--surface-2);
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    font-size: 0.875rem;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.class-btn:hover {
    background: var(--surface-3);
}

.class-btn.active {
    border-color: var(--text-tertiary);
    color: var(--text-primary);
}

.class-indicator {
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.class-indicator.class-a {
    background: var(--class-a);
}

.class-indicator.class-b {
    background: var(--class-b);
}

.slider-container {
    display: flex;
    flex-direction: column;
    gap: var(--space-xs);
}

.slider {
    -webkit-appearance: none;
    width: 100%;
    height: 6px;
    background: var(--surface-3);
    border-radius: 3px;
    outline: none;
}

.slider::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 18px;
    height: 18px;
    background: var(--accent-gold);
    border-radius: 50%;
    cursor: pointer;
    transition: transform var(--transition-fast);
}

.slider::-webkit-slider-thumb:hover {
    transform: scale(1.1);
}

.slider-labels {
    display: flex;
    justify-content: space-between;
    font-size: 0.7rem;
    color: var(--text-muted);
}

.control-actions {
    display: flex;
    gap: var(--space-sm);
    align-items: flex-end;
}

.btn {
    padding: var(--space-sm) var(--space-lg);
    border-radius: var(--radius-md);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    border: none;
}

.btn-primary {
    background: var(--accent-gold);
    color: var(--bg-primary);
}

.btn-primary:hover {
    background: var(--accent-gold-dim);
    box-shadow: var(--shadow-glow);
}

.btn-secondary {
    background: var(--surface-3);
    color: var(--text-secondary);
    border: 1px solid var(--surface-3);
}

.btn-secondary:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.btn-ghost {
    background: transparent;
    color: var(--text-tertiary);
    border: 1px solid var(--surface-3);
}

.btn-ghost:hover {
    background: var(--surface-2);
    color: var(--text-secondary);
}

.lab-canvas-container {
    position: relative;
    display: flex;
    justify-content: center;
    background: var(--bg-primary);
    border-radius: var(--radius-md);
    overflow: hidden;
}

#decision-boundary-canvas {
    display: block;
    cursor: crosshair;
}

.canvas-instructions {
    position: absolute;
    bottom: var(--space-md);
    left: 50%;
    transform: translateX(-50%);
    font-size: 0.75rem;
    color: var(--text-muted);
    background: rgba(13, 15, 18, 0.8);
    padding: var(--space-xs) var(--space-md);
    border-radius: var(--radius-sm);
}

.lab-metrics {
    display: flex;
    justify-content: center;
    gap: var(--space-2xl);
    margin-top: var(--space-xl);
    padding-top: var(--space-xl);
    border-top: 1px solid var(--surface-2);
}

.metric {
    text-align: center;
}

.metric-value {
    display: block;
    font-family: var(--font-mono);
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--accent-gold);
}

.metric-label {
    font-size: 0.75rem;
    color: var(--text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.lab-insights {
    margin-top: var(--space-xl);
    padding: var(--space-lg);
    background: var(--surface-1);
    border-radius: var(--radius-md);
}

.lab-insights h4 {
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--space-md);
}

.lab-insights ul {
    list-style: none;
}

.lab-insights li {
    position: relative;
    padding-left: var(--space-lg);
    margin-bottom: var(--space-md);
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.lab-insights li::before {
    content: '→';
    position: absolute;
    left: 0;
    color: var(--accent-gold-dim);
}

.lab-insights li:last-child {
    margin-bottom: 0;
}

.lab-insights strong {
    color: var(--text-primary);
}

/* ============================================
   Quiz Section
   ============================================ */
.quiz-container {
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
}

.quiz-question {
    margin-bottom: var(--space-xl);
    padding-bottom: var(--space-xl);
    border-bottom: 1px solid var(--surface-2);
}

.quiz-question:last-of-type {
    border-bottom: none;
    padding-bottom: 0;
    margin-bottom: var(--space-lg);
}

.question-header {
    display: flex;
    gap: var(--space-md);
    margin-bottom: var(--space-md);
}

.question-number {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 28px;
    height: 28px;
    background: var(--surface-3);
    border-radius: 50%;
    font-family: var(--font-mono);
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    flex-shrink: 0;
}

.question-text {
    font-size: 1rem;
    color: var(--text-primary);
    line-height: 1.6;
}

.question-options {
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
    margin-left: calc(28px + var(--space-md));
}

.option {
    display: flex;
    align-items: flex-start;
    gap: var(--space-md);
    padding: var(--space-md);
    background: var(--surface-2);
    border: 1px solid transparent;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.option:hover {
    background: var(--surface-3);
}

.option input {
    display: none;
}

.option-marker {
    width: 18px;
    height: 18px;
    border: 2px solid var(--text-muted);
    border-radius: 50%;
    flex-shrink: 0;
    margin-top: 2px;
    transition: all var(--transition-fast);
    position: relative;
}

.option input:checked+.option-marker {
    border-color: var(--accent-gold);
    background: var(--accent-gold);
}

.option input:checked+.option-marker::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 6px;
    height: 6px;
    background: var(--bg-primary);
    border-radius: 50%;
}

.option-text {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

.option input:checked~.option-text {
    color: var(--text-primary);
}

.option.correct {
    background: var(--success-bg);
    border-color: var(--success);
}

.option.correct .option-marker {
    border-color: var(--success);
    background: var(--success);
}

.option.incorrect {
    background: var(--error-bg);
    border-color: var(--error);
}

.option.incorrect .option-marker {
    border-color: var(--error);
    background: var(--error);
}

.question-feedback {
    margin-top: var(--space-md);
    margin-left: calc(28px + var(--space-md));
    padding: var(--space-md);
    border-radius: var(--radius-md);
    font-size: 0.875rem;
    display: none;
}

.question-feedback.show {
    display: block;
}

.question-feedback.correct {
    background: var(--success-bg);
    color: var(--success);
}

.question-feedback.incorrect {
    background: var(--error-bg);
    color: var(--text-secondary);
}

.quiz-actions {
    display: flex;
    gap: var(--space-md);
    margin-top: var(--space-xl);
    padding-top: var(--space-lg);
    border-top: 1px solid var(--surface-2);
}

.quiz-results {
    display: none;
    text-align: center;
    padding: var(--space-xl);
    background: var(--bg-tertiary);
    border-radius: var(--radius-md);
    margin-top: var(--space-lg);
}

.quiz-results.show {
    display: block;
}

.results-score {
    margin-bottom: var(--space-md);
}

.score-value {
    font-family: var(--font-mono);
    font-size: 3rem;
    font-weight: 700;
    color: var(--accent-gold);
}

.score-total {
    font-size: 1.5rem;
    color: var(--text-tertiary);
}

.results-message {
    color: var(--text-secondary);
    font-size: 1rem;
}

/* ============================================
   Module Navigation
   ============================================ */
.module-navigation {
    display: flex;
    justify-content: space-between;
    gap: var(--space-lg);
    margin-top: var(--space-3xl);
    padding-top: var(--space-2xl);
    border-top: 1px solid var(--surface-2);
}

.nav-prev,
.nav-next {
    flex: 1;
    padding: var(--space-lg);
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-base);
}

.nav-prev:hover:not(.disabled),
.nav-next:hover {
    background: var(--surface-2);
    border-color: var(--surface-3);
}

.nav-prev.disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.nav-prev {
    text-align: left;
}

.nav-next {
    text-align: right;
}

.nav-direction {
    display: block;
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-tertiary);
    margin-bottom: var(--space-xs);
}

.nav-title {
    font-family: var(--font-display);
    font-size: 1rem;
    color: var(--text-primary);
}

/* Navigation Links */
.nav-link {
    display: flex;
    align-items: baseline;
    gap: var(--space-md);
    text-decoration: none;
    color: inherit;
    width: 100%;
}

a.nav-prev,
a.nav-next {
    text-decoration: none;
    color: inherit;
}

/* ============================================
   Animations
   ============================================ */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes pulse {

    0%,
    100% {
        opacity: 1;
    }

    50% {
        opacity: 0.7;
    }
}

.module-content>section {
    animation: fadeIn 0.5s ease forwards;
}

.module-content>section:nth-child(1) {
    animation-delay: 0s;
}

.module-content>section:nth-child(2) {
    animation-delay: 0.1s;
}

.module-content>section:nth-child(3) {
    animation-delay: 0.15s;
}

.module-content>section:nth-child(4) {
    animation-delay: 0.2s;
}

.module-content>section:nth-child(5) {
    animation-delay: 0.25s;
}

.module-content>section:nth-child(6) {
    animation-delay: 0.3s;
}

.module-content>section:nth-child(7) {
    animation-delay: 0.35s;
}

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 1200px) {
    :root {
        --sidebar-width: 280px;
    }
}

@media (max-width: 1024px) {

    /* Hide old mobile header - using new sidebar toggle instead */
    .mobile-header {
        display: none !important;
    }

    .hamburger-btn {
        display: none;
    }

    /* Show overlay when sidebar is open */
    .sidebar-overlay.active {
        display: block;
    }

    /* Sidebar positioning handled by sidebar-collapsed class */
    .sidebar {
        box-shadow: none;
    }

    .sidebar.open {
        transform: translateX(0);
        box-shadow: var(--shadow-lg);
    }

    /* Adjust main content */
    .main-content {
        margin-left: 0;
        padding-top: var(--header-height);
    }

    /* Hide desktop header elements on mobile */
    .content-header {
        top: var(--header-height);
    }

    .taxonomy-ring.ring-ai {
        width: 340px;
        height: 340px;
    }

    .taxonomy-ring.ring-ml {
        width: 240px;
        height: 240px;
    }

    .taxonomy-ring.ring-dl {
        width: 130px;
        height: 130px;
    }
}

@media (max-width: 768px) {
    :root {
        --sidebar-width: 100%;
    }

    .sidebar {
        width: 85%;
        max-width: 320px;
    }

    .module-title {
        font-size: 1.75rem;
    }

    .module-subtitle {
        font-size: 1rem;
    }

    .module-content {
        padding: var(--space-xl) var(--space-md);
    }

    .content-header {
        padding: var(--space-sm) var(--space-md);
    }

    .lab-section {
        margin-left: calc(-1 * var(--space-md));
        margin-right: calc(-1 * var(--space-md));
        padding: var(--space-lg) var(--space-md);
        border-radius: 0;
    }

    .lab-controls {
        flex-direction: column;
        gap: var(--space-md);
    }

    .control-group {
        min-width: 100%;
    }

    .control-actions {
        flex-wrap: wrap;
        justify-content: stretch;
    }

    .control-actions .btn {
        flex: 1;
        min-width: 120px;
    }

    #decision-boundary-canvas {
        width: 100%;
        height: auto;
        aspect-ratio: 1;
        max-height: 350px;
    }

    .lab-metrics {
        flex-wrap: wrap;
        gap: var(--space-md);
        justify-content: space-around;
    }

    .metric {
        min-width: 80px;
    }

    .taxonomy-visual {
        display: none;
    }

    .module-navigation {
        flex-direction: column;
    }

    /* Definition blocks */
    .definition-block {
        padding: var(--space-lg);
    }

    .definition-text {
        font-size: 1rem;
    }

    /* Key insight */
    .key-insight {
        flex-direction: column;
        gap: var(--space-md);
        padding: var(--space-lg);
    }

    .insight-icon {
        font-size: 1.25rem;
    }

    /* Layers */
    .explanation-layers {
        gap: var(--space-md);
    }

    .layer {
        padding: var(--space-lg);
    }

    /* Quiz */
    .question-options {
        margin-left: 0;
        margin-top: var(--space-md);
    }

    .quiz-container {
        padding: var(--space-lg);
    }

    /* Section headings */
    .section-heading {
        font-size: 1.35rem;
    }

    /* Learning objectives */
    .learning-objectives {
        padding: var(--space-lg);
    }

    /* Tables */
    table {
        font-size: 0.8rem;
    }

    th,
    td {
        padding: var(--space-sm);
    }

    /* ML Types Grid */
    .ml-types-grid {
        grid-template-columns: 1fr;
    }

    /* Prerequisite grid */
    .prereq-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .module-title {
        font-size: 1.5rem;
    }

    .module-hero {
        margin-bottom: var(--space-xl);
        padding-bottom: var(--space-lg);
    }

    .module-meta {
        flex-direction: column;
        gap: var(--space-sm);
    }

    .btn {
        padding: var(--space-md) var(--space-lg);
        font-size: 0.9rem;
    }

    .metric-value {
        font-size: 1.25rem;
    }

    .class-selector {
        flex-direction: column;
    }

    /* Concept cards */
    .concept-card {
        padding: var(--space-lg);
    }

    .concept-title {
        font-size: 1.1rem;
    }

    /* Misconception cards */
    .misconception-card {
        padding: var(--space-lg);
    }

    .misconception-body {
        padding-left: 0;
    }
}

/* Touch-friendly adjustments */
@media (hover: none) and (pointer: coarse) {
    .nav-item {
        padding: var(--space-md) var(--space-xl);
    }

    .btn {
        min-height: 48px;
    }

    .option {
        padding: var(--space-lg);
    }

    .theme-toggle,
    .hamburger-btn {
        width: 48px;
        height: 48px;
    }

    .slider::-webkit-slider-thumb {
        width: 24px;
        height: 24px;
    }
}

/* ============================================
   ML Types Taxonomy Grid
   ============================================ */

.ml-types-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--space-lg);
    margin: var(--space-xl) 0;
}

.ml-type-card {
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-md);
    overflow: hidden;
    transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.ml-type-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.3);
}

.ml-type-header {
    padding: var(--space-md) var(--space-lg);
    border-bottom: 2px solid transparent;
}

.ml-type-header h4 {
    margin: 0;
    font-family: var(--font-display);
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.ml-type-header.supervised {
    background: rgba(78, 205, 196, 0.1);
    border-color: #4ECDC4;
}

.ml-type-header.unsupervised {
    background: rgba(139, 92, 246, 0.1);
    border-color: #8B5CF6;
}

.ml-type-header.reinforcement {
    background: rgba(212, 168, 85, 0.1);
    border-color: var(--accent-gold);
}

.ml-type-header.self-supervised {
    background: rgba(91, 155, 213, 0.1);
    border-color: var(--accent-blue);
}

.ml-type-header.semi-supervised {
    background: rgba(224, 122, 95, 0.1);
    border-color: var(--accent-coral);
}

.ml-type-content {
    padding: var(--space-lg);
}

.ml-type-def {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.ml-type-how {
    font-size: 0.85rem;
    color: var(--text-tertiary);
    background: var(--bg-tertiary);
    padding: var(--space-sm) var(--space-md);
    border-radius: var(--radius-sm);
    margin-bottom: var(--space-md);
}

.ml-type-examples {
    margin-bottom: var(--space-md);
}

.ml-type-examples strong {
    display: block;
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-xs);
}

.ml-type-examples ul {
    margin: 0;
    padding-left: var(--space-lg);
}

.ml-type-examples li {
    font-size: 0.85rem;
    color: var(--text-tertiary);
    margin-bottom: var(--space-xs);
}

.ml-type-note {
    font-size: 0.8rem;
    color: var(--accent-gold);
    font-style: italic;
    margin: 0;
}

/* ============================================
   Prerequisites Banner
   ============================================ */

.prerequisites-banner {
    background: linear-gradient(135deg, var(--surface-1), var(--bg-tertiary));
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-lg);
    margin: var(--space-lg) 0 var(--space-xl);
    overflow: hidden;
}

.prereq-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--space-lg) var(--space-xl);
    cursor: pointer;
}

.prereq-header h2 {
    font-family: var(--font-display);
    font-size: 1.1rem;
    color: var(--text-primary);
    margin: 0;
}

.prereq-toggle {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    background: var(--surface-2);
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-sm);
    padding: var(--space-sm) var(--space-md);
    color: var(--text-secondary);
    font-size: 0.85rem;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.prereq-toggle:hover {
    background: var(--surface-3);
}

.toggle-icon {
    transition: transform var(--transition-fast);
}

.prerequisites-banner.expanded .toggle-icon {
    transform: rotate(180deg);
}

.prerequisites-banner.expanded .toggle-text::before {
    content: 'Hide ';
}

.prerequisites-banner:not(.expanded) .toggle-text::before {
    content: 'Show ';
}

.prereq-content {
    display: none;
    padding: 0 var(--space-xl) var(--space-xl);
}

.prerequisites-banner.expanded .prereq-content {
    display: block;
}

.prereq-intro {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-lg);
}

.prereq-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--space-lg);
    margin-bottom: var(--space-lg);
}

.prereq-card {
    background: var(--surface-1);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius-md);
    padding: var(--space-lg);
}

.prereq-card h3 {
    font-family: var(--font-display);
    font-size: 1rem;
    color: var(--text-primary);
    margin-bottom: var(--space-md);
}

.prereq-card ul {
    margin: 0 0 var(--space-md);
    padding-left: var(--space-lg);
}

.prereq-card li {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-xs);
}

.prereq-card a {
    color: var(--accent-gold);
    text-decoration: none;
}

.prereq-card a:hover {
    text-decoration: underline;
}

.prereq-level {
    font-size: 0.8rem;
    color: var(--text-tertiary);
    font-style: italic;
    margin: 0;
}

.prereq-links {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-sm);
    margin-top: var(--space-md);
    padding-top: var(--space-md);
    border-top: 1px solid var(--surface-2);
}

.prereq-link-btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-xs);
    padding: var(--space-xs) var(--space-md);
    background: var(--bg-tertiary);
    border: 1px solid var(--surface-3);
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-size: 0.75rem;
    font-weight: 500;
    text-decoration: none;
    transition: all var(--transition-fast);
}

.prereq-link-btn:hover {
    background: var(--accent-gold-glow);
    border-color: var(--accent-gold);
    color: var(--accent-gold);
    transform: translateY(-1px);
    text-decoration: none;
}

/* Beginner prereq link variant */
.prereq-link-btn.prereq-link-beginner {
    background: linear-gradient(135deg, rgba(139, 92, 246, 0.1) 0%, rgba(139, 92, 246, 0.05) 100%);
    border-color: rgba(139, 92, 246, 0.3);
    color: #a78bfa;
}

.prereq-link-btn.prereq-link-beginner:hover {
    background: rgba(139, 92, 246, 0.2);
    border-color: #a78bfa;
    color: #c4b5fd;
}

/* Prerequisite level groups */
.prereq-level-group {
    margin-bottom: var(--space-lg);
    padding-bottom: var(--space-md);
    border-bottom: 1px solid var(--surface-2);
}

.prereq-level-group:last-of-type {
    margin-bottom: var(--space-sm);
    padding-bottom: 0;
    border-bottom: none;
}

.prereq-sublevel {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.075em;
    margin: 0 0 var(--space-sm);
    padding: var(--space-xs) var(--space-sm);
    background: var(--bg-tertiary);
    border-radius: var(--radius-sm);
    display: inline-block;
}

.prereq-level-group ul {
    margin-top: var(--space-sm);
}

.prereq-level-group .prereq-links {
    margin-top: var(--space-md);
}

.prereq-self-check {
    background: var(--bg-tertiary);
    border-radius: var(--radius-md);
    padding: var(--space-lg);
}

.prereq-self-check h4 {
    font-size: 0.95rem;
    color: var(--text-primary);
    margin-bottom: var(--space-sm);
}

.prereq-self-check>p {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: var(--space-md);
}

.self-check-list {
    margin: 0;
    padding-left: var(--space-lg);
}

.self-check-list li {
    font-size: 0.85rem;
    color: var(--text-tertiary);
    margin-bottom: var(--space-xs);
}

/* Scrollbar Styling */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
}

::-webkit-scrollbar-thumb {
    background: var(--surface-3);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* Selection */
::selection {
    background: var(--accent-gold-glow);
    color: var(--text-primary);
}

/* Focus States for Accessibility */
:focus-visible {
    outline: 2px solid var(--accent-gold);
    outline-offset: 2px;
}

button:focus-visible,
a:focus-visible,
input:focus-visible,
select:focus-visible {
    outline: 2px solid var(--accent-gold);
    outline-offset: 2px;
}

/* Skip Link for Accessibility */
.skip-link {
    position: absolute;
    top: -100px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--accent-gold);
    color: var(--bg-primary);
    padding: var(--space-sm) var(--space-lg);
    border-radius: var(--radius-md);
    z-index: 9999;
    font-weight: 600;
    text-decoration: none;
    transition: top var(--transition-fast);
}

.skip-link:focus {
    top: var(--space-md);
}

/* ============================================
   Scroll Progress Indicator
   ============================================ */
.scroll-progress {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    z-index: 1000;
    background: transparent;
}

.scroll-progress-bar {
    height: 100%;
    width: 0;
    background: linear-gradient(90deg, var(--accent-gold-dim), var(--accent-gold));
    transition: width 50ms ease-out;
}

@media (max-width: 1024px) {
    .scroll-progress {
        top: var(--header-height);
    }
}

/* ============================================
   Back to Top Button
   ============================================ */
.back-to-top {
    position: fixed;
    bottom: var(--space-xl);
    right: var(--space-xl);
    width: 48px;
    height: 48px;
    background: var(--accent-gold);
    color: var(--bg-primary);
    border: none;
    border-radius: 50%;
    font-size: 1.25rem;
    font-weight: 700;
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px);
    transition: all var(--transition-base);
    z-index: 100;
    box-shadow: var(--shadow-md);
}

.back-to-top:hover {
    background: var(--accent-gold-dim);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

@media (max-width: 768px) {
    .back-to-top {
        bottom: var(--space-lg);
        right: var(--space-lg);
        width: 44px;
        height: 44px;
    }
}

/* ============================================
   Print Styles
   ============================================ */
@media print {

    .sidebar,
    .mobile-header,
    .back-to-top,
    .scroll-progress,
    .lab-section,
    .quiz-section,
    .module-navigation {
        display: none !important;
    }

    .main-content {
        margin-left: 0 !important;
        padding-top: 0 !important;
    }

    .module-content {
        max-width: 100%;
    }

    body {
        background: white;
        color: black;
    }
}