/* ============================================================
   Windows Server Academy — Design System
   ============================================================ */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;500;600&display=swap');

/* --- CSS Custom Properties (Light Theme) --- */
:root {
  /* Brand */
  --primary: #0078D4;
  --primary-hover: #106EBE;
  --primary-light: #DEECF9;
  --accent: #50E6FF;
  --accent-warm: #FFB900;

  /* Surfaces */
  --bg-root: #F3F4F8;
  --bg-surface: #FFFFFF;
  --bg-surface-hover: #F9FAFB;
  --bg-elevated: #FFFFFF;
  --bg-sidebar: #FAFAFC;
  --bg-code: #F0F2F5;
  --bg-hero: linear-gradient(135deg, #0078D4 0%, #005A9E 50%, #003D6B 100%);

  /* Text */
  --text-primary: #1A1A2E;
  --text-secondary: #4A5568;
  --text-tertiary: #718096;
  --text-inverse: #FFFFFF;
  --text-link: #0078D4;
  --text-code: #D63384;

  /* Borders */
  --border: #E2E8F0;
  --border-hover: #CBD5E0;
  --border-focus: #0078D4;

  /* Semantic */
  --success: #10B981;
  --success-bg: #D1FAE5;
  --warning: #F59E0B;
  --warning-bg: #FEF3C7;
  --error: #EF4444;
  --error-bg: #FEE2E2;
  --info: #3B82F6;
  --info-bg: #DBEAFE;
  --tip-bg: #E0F7FA;
  --tip: #0097A7;

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 60px rgba(0, 0, 0, 0.12);
  --shadow-glow: 0 0 20px rgba(0, 120, 212, 0.15);

  /* Glassmorphism */
  --glass-bg: rgba(255, 255, 255, 0.7);
  --glass-border: rgba(255, 255, 255, 0.3);
  --glass-blur: 12px;

  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-full: 9999px;

  /* Spacing */
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;
  --space-2xl: 48px;
  --space-3xl: 64px;

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Cascadia Code', 'Consolas', monospace;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.8125rem;
  --font-size-base: 0.9375rem;
  --font-size-md: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.3125rem;
  --font-size-2xl: 1.625rem;
  --font-size-3xl: 2rem;
  --font-size-4xl: 2.5rem;
  --font-size-5xl: 3.25rem;
  --line-height: 1.7;

  /* Layout */
  --sidebar-width: 300px;
  --sidebar-collapsed: 0px;
  --header-height: 60px;
  --content-max-width: 880px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;
  --transition-spring: 500ms cubic-bezier(0.34, 1.56, 0.64, 1);
}

/* --- Dark Theme --- */
[data-theme="dark"] {
  --bg-root: #0B0D17;
  --bg-surface: #131627;
  --bg-surface-hover: #1A1D35;
  --bg-elevated: #1E2140;
  --bg-sidebar: #0E1020;
  --bg-code: #1A1D35;
  --bg-hero: linear-gradient(135deg, #0E1020 0%, #0078D4 50%, #50E6FF 100%);

  --text-primary: #E8ECF4;
  --text-secondary: #A0AEC0;
  --text-tertiary: #718096;
  --text-link: #50E6FF;
  --text-code: #FF79C6;

  --border: #2D3154;
  --border-hover: #3D4270;
  --border-focus: #50E6FF;

  --success-bg: #064E3B;
  --warning-bg: #78350F;
  --error-bg: #7F1D1D;
  --info-bg: #1E3A5F;
  --tip-bg: #0D3B44;

  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.5);
  --shadow-xl: 0 20px 60px rgba(0, 0, 0, 0.6);
  --shadow-glow: 0 0 30px rgba(80, 230, 255, 0.1);

  --glass-bg: rgba(19, 22, 39, 0.8);
  --glass-border: rgba(45, 49, 84, 0.5);
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  font-size: 16px;
}

body {
  font-family: var(--font-sans);
  font-size: var(--font-size-base);
  line-height: var(--line-height);
  color: var(--text-primary);
  background: var(--bg-root);
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

a {
  color: var(--text-link);
  text-decoration: none;
  transition: color var(--transition-fast);
}
a:hover { color: var(--primary-hover); }
[data-theme="dark"] a:hover { color: var(--accent); }

img { max-width: 100%; display: block; }
button { cursor: pointer; font-family: inherit; }

::selection {
  background: var(--primary);
  color: var(--text-inverse);
}

/* Custom scrollbar */
::-webkit-scrollbar { width: 7px; height: 7px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb {
  background: var(--border-hover);
  border-radius: var(--radius-full);
}
::-webkit-scrollbar-thumb:hover { background: var(--text-tertiary); }

/* ============================================================
   LAYOUT
   ============================================================ */

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

/* --- Header (Mobile) --- */
.mobile-header {
  display: none;
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--header-height);
  background: var(--glass-bg);
  backdrop-filter: blur(var(--glass-blur));
  -webkit-backdrop-filter: blur(var(--glass-blur));
  border-bottom: 1px solid var(--border);
  z-index: 1000;
  padding: 0 var(--space-md);
  align-items: center;
  justify-content: space-between;
}

.mobile-header .logo-sm {
  font-weight: 700;
  font-size: var(--font-size-lg);
  color: var(--primary);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.hamburger {
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  padding: var(--space-sm);
  border-radius: var(--radius-sm);
  transition: background var(--transition-fast);
}
.hamburger:hover { background: var(--bg-surface-hover); }

/* --- Sidebar --- */
.sidebar {
  width: var(--sidebar-width);
  height: 100vh;
  position: fixed;
  top: 0;
  left: 0;
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  z-index: 900;
  transition: transform var(--transition-base);
  overflow: hidden;
}

.sidebar-header {
  padding: var(--space-lg) var(--space-lg) var(--space-md);
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.sidebar-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: var(--font-size-xl);
  font-weight: 800;
  color: var(--primary);
  letter-spacing: -0.02em;
}

.sidebar-logo .logo-icon {
  width: 32px;
  height: 32px;
  background: var(--bg-hero);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: var(--font-size-sm);
  font-weight: 700;
}

.sidebar-subtitle {
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-top: var(--space-xs);
}

/* Sidebar search */
.sidebar-search {
  padding: var(--space-md) var(--space-lg);
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.sidebar-search input {
  width: 100%;
  padding: var(--space-sm) var(--space-md);
  padding-left: 36px;
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: var(--font-size-sm);
  font-family: var(--font-sans);
  transition: all var(--transition-fast);
  outline: none;
}

.sidebar-search input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(0, 120, 212, 0.15);
}

.sidebar-search .search-wrapper {
  position: relative;
}

.sidebar-search .search-icon {
  position: absolute;
  left: 10px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-tertiary);
  font-size: var(--font-size-sm);
  pointer-events: none;
}

/* Sidebar navigation */
.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: var(--space-sm) 0;
}

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

.nav-section-title {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-sm) var(--space-lg);
  font-size: var(--font-size-sm);
  font-weight: 600;
  color: var(--text-secondary);
  cursor: pointer;
  user-select: none;
  transition: all var(--transition-fast);
  border: none;
  background: none;
  width: 100%;
  text-align: left;
}

.nav-section-title:hover {
  color: var(--text-primary);
  background: var(--bg-surface-hover);
}

.nav-section-title .section-progress {
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
  font-weight: 400;
}

.nav-section-title .chevron {
  font-size: 10px;
  transition: transform var(--transition-fast);
  color: var(--text-tertiary);
}

.nav-section.collapsed .chevron {
  transform: rotate(-90deg);
}

.nav-section.collapsed .nav-items {
  display: none;
}

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

.nav-item {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 6px var(--space-lg) 6px calc(var(--space-lg) + 12px);
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
  border-left: 3px solid transparent;
  text-decoration: none;
  position: relative;
}

.nav-item:hover {
  background: var(--bg-surface-hover);
  color: var(--text-primary);
}

.nav-item.active {
  background: var(--primary-light);
  color: var(--primary);
  border-left-color: var(--primary);
  font-weight: 500;
}

[data-theme="dark"] .nav-item.active {
  background: rgba(0, 120, 212, 0.15);
  color: var(--accent);
  border-left-color: var(--accent);
}

.nav-item .check-icon {
  font-size: 12px;
  color: var(--success);
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.nav-item.completed .check-icon {
  opacity: 1;
}

/* Sidebar footer */
.sidebar-footer {
  padding: var(--space-md) var(--space-lg);
  border-top: 1px solid var(--border);
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.theme-toggle {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-full);
  color: var(--text-secondary);
  font-size: var(--font-size-sm);
  transition: all var(--transition-fast);
}

.theme-toggle:hover {
  border-color: var(--border-hover);
  color: var(--text-primary);
}

.overall-progress {
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
}

.overall-progress-bar {
  width: 100%;
  height: 4px;
  background: var(--border);
  border-radius: var(--radius-full);
  margin-top: var(--space-xs);
  overflow: hidden;
}

.overall-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: var(--radius-full);
  transition: width var(--transition-slow);
  width: 0%;
}

/* --- Main Content --- */
.main-content {
  flex: 1;
  margin-left: var(--sidebar-width);
  min-height: 100vh;
  transition: margin-left var(--transition-base);
}

/* --- Overlay (mobile sidebar) --- */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  z-index: 850;
  opacity: 0;
  transition: opacity var(--transition-base);
}

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

/* ============================================================
   HERO / HOME
   ============================================================ */
.hero {
  background: var(--bg-hero);
  padding: var(--space-3xl) var(--space-2xl);
  color: white;
  position: relative;
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(80, 230, 255, 0.15) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

.hero::after {
  content: '';
  position: absolute;
  bottom: -30%;
  left: -10%;
  width: 400px;
  height: 400px;
  background: radial-gradient(circle, rgba(255, 185, 0, 0.1) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}

.hero-content {
  max-width: var(--content-max-width);
  margin: 0 auto;
  position: relative;
  z-index: 1;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-xs) var(--space-md);
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(8px);
  border-radius: var(--radius-full);
  font-size: var(--font-size-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: var(--space-lg);
  border: 1px solid rgba(255, 255, 255, 0.2);
}

.hero h1 {
  font-size: var(--font-size-5xl);
  font-weight: 900;
  line-height: 1.1;
  margin-bottom: var(--space-md);
  letter-spacing: -0.03em;
}

.hero h1 .gradient-text {
  background: linear-gradient(135deg, #50E6FF, #FFB900);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero p {
  font-size: var(--font-size-lg);
  opacity: 0.9;
  max-width: 600px;
  line-height: 1.7;
  margin-bottom: var(--space-xl);
}

.hero-stats {
  display: flex;
  gap: var(--space-xl);
  flex-wrap: wrap;
}

.hero-stat {
  text-align: center;
}

.hero-stat .stat-number {
  display: block;
  font-size: var(--font-size-3xl);
  font-weight: 800;
  line-height: 1;
}

.hero-stat .stat-label {
  font-size: var(--font-size-xs);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  opacity: 0.7;
  margin-top: var(--space-xs);
  display: block;
}

.hero-actions {
  display: flex;
  gap: var(--space-md);
  margin-top: var(--space-xl);
  flex-wrap: wrap;
}

/* ============================================================
   BUTTONS
   ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 10px 24px;
  border-radius: var(--radius-md);
  font-size: var(--font-size-sm);
  font-weight: 600;
  border: none;
  transition: all var(--transition-fast);
  text-decoration: none;
  white-space: nowrap;
}

.btn-primary {
  background: white;
  color: var(--primary);
}
.btn-primary:hover {
  background: #F0F0F0;
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  color: var(--primary);
}

.btn-outline {
  background: transparent;
  color: white;
  border: 2px solid rgba(255, 255, 255, 0.4);
}
.btn-outline:hover {
  background: rgba(255, 255, 255, 0.1);
  border-color: white;
  color: white;
}

.btn-sm {
  padding: 6px 14px;
  font-size: var(--font-size-xs);
}

.btn-accent {
  background: var(--primary);
  color: white;
}
.btn-accent:hover {
  background: var(--primary-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  color: white;
}

.btn-ghost {
  background: transparent;
  color: var(--text-secondary);
  border: 1px solid var(--border);
}
.btn-ghost:hover {
  background: var(--bg-surface-hover);
  color: var(--text-primary);
  border-color: var(--border-hover);
}

.btn-success {
  background: var(--success);
  color: white;
}
.btn-success:hover {
  filter: brightness(1.1);
  transform: translateY(-1px);
}

/* ============================================================
   CONTENT PAGES
   ============================================================ */
.page-content {
  max-width: var(--content-max-width);
  margin: 0 auto;
  padding: var(--space-2xl);
}

/* --- Section page (home, roadmap, etc) --- */
.section-page {
  animation: fadeInUp 0.4s ease;
}

/* --- Lesson View --- */
.lesson-view {
  animation: fadeInUp 0.4s ease;
}

.lesson-breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: var(--font-size-sm);
  color: var(--text-tertiary);
  margin-bottom: var(--space-lg);
}

.lesson-breadcrumb a {
  color: var(--text-tertiary);
}
.lesson-breadcrumb a:hover { color: var(--text-link); }
.lesson-breadcrumb .sep { opacity: 0.4; }

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

.lesson-module-tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  background: var(--primary-light);
  color: var(--primary);
  border-radius: var(--radius-full);
  font-size: var(--font-size-xs);
  font-weight: 600;
  margin-bottom: var(--space-md);
}

[data-theme="dark"] .lesson-module-tag {
  background: rgba(0, 120, 212, 0.2);
  color: var(--accent);
}

.lesson-header h1 {
  font-size: var(--font-size-3xl);
  font-weight: 800;
  letter-spacing: -0.02em;
  margin-bottom: var(--space-sm);
  line-height: 1.2;
}

.lesson-meta {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
  flex-wrap: wrap;
  color: var(--text-tertiary);
  font-size: var(--font-size-sm);
}

.lesson-meta span {
  display: flex;
  align-items: center;
  gap: 4px;
}

/* Lesson body */
.lesson-body h2 {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  margin-top: var(--space-2xl);
  margin-bottom: var(--space-md);
  padding-bottom: var(--space-sm);
  border-bottom: 2px solid var(--border);
  letter-spacing: -0.01em;
}

.lesson-body h3 {
  font-size: var(--font-size-xl);
  font-weight: 600;
  margin-top: var(--space-xl);
  margin-bottom: var(--space-md);
  color: var(--text-primary);
}

.lesson-body h4 {
  font-size: var(--font-size-md);
  font-weight: 600;
  margin-top: var(--space-lg);
  margin-bottom: var(--space-sm);
}

.lesson-body p {
  margin-bottom: var(--space-md);
  color: var(--text-secondary);
  line-height: 1.8;
}

.lesson-body ul, .lesson-body ol {
  margin-bottom: var(--space-md);
  padding-left: var(--space-lg);
  color: var(--text-secondary);
}

.lesson-body li {
  margin-bottom: var(--space-sm);
  line-height: 1.7;
}

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

/* Tables */
.lesson-body table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-lg) 0;
  font-size: var(--font-size-sm);
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border);
}

.lesson-body th {
  background: var(--bg-code);
  font-weight: 600;
  text-align: left;
  padding: 12px 16px;
  color: var(--text-primary);
  border-bottom: 2px solid var(--border);
}

.lesson-body td {
  padding: 10px 16px;
  border-bottom: 1px solid var(--border);
  color: var(--text-secondary);
}

.lesson-body tr:last-child td {
  border-bottom: none;
}

.lesson-body tr:hover td {
  background: var(--bg-surface-hover);
}

/* --- Code Blocks --- */
.code-block {
  position: relative;
  margin: var(--space-lg) 0;
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border);
}

.code-block-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-sm) var(--space-md);
  background: var(--bg-code);
  border-bottom: 1px solid var(--border);
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
}

.code-block-header .lang-tag {
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.copy-btn {
  display: flex;
  align-items: center;
  gap: 4px;
  padding: 3px 10px;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text-tertiary);
  font-size: var(--font-size-xs);
  font-family: var(--font-sans);
  transition: all var(--transition-fast);
}

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

.copy-btn.copied {
  color: var(--success);
  border-color: var(--success);
}

.code-block pre {
  padding: var(--space-md);
  overflow-x: auto;
  background: var(--bg-surface);
  margin: 0;
}

.code-block code {
  font-family: var(--font-mono);
  font-size: var(--font-size-sm);
  line-height: 1.6;
  color: var(--text-primary);
}

/* Inline code */
.lesson-body code:not(.code-block code) {
  padding: 2px 6px;
  background: var(--bg-code);
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.85em;
  color: var(--text-code);
  border: 1px solid var(--border);
}

/* ============================================================
   CALLOUT BOXES
   ============================================================ */
.callout {
  padding: var(--space-md) var(--space-lg);
  border-radius: var(--radius-md);
  margin: var(--space-lg) 0;
  border-left: 4px solid;
  font-size: var(--font-size-sm);
}

.callout-title {
  font-weight: 700;
  margin-bottom: var(--space-sm);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: var(--font-size-base);
}

.callout-info {
  background: var(--info-bg);
  border-color: var(--info);
}
.callout-info .callout-title { color: var(--info); }

.callout-tip {
  background: var(--tip-bg);
  border-color: var(--tip);
}
.callout-tip .callout-title { color: var(--tip); }

.callout-warning {
  background: var(--warning-bg);
  border-color: var(--warning);
}
.callout-warning .callout-title { color: var(--warning); }

.callout-danger {
  background: var(--error-bg);
  border-color: var(--error);
}
.callout-danger .callout-title { color: var(--error); }

.callout-success {
  background: var(--success-bg);
  border-color: var(--success);
}
.callout-success .callout-title { color: var(--success); }

.callout p {
  color: var(--text-secondary);
  margin: 0;
}

/* ============================================================
   CARDS
   ============================================================ */
.card {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  transition: all var(--transition-base);
}

.card:hover {
  border-color: var(--border-hover);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.card-glass {
  background: var(--glass-bg);
  backdrop-filter: blur(var(--glass-blur));
  -webkit-backdrop-filter: blur(var(--glass-blur));
  border: 1px solid var(--glass-border);
}

/* Module cards (home page) */
.module-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--space-lg);
  margin-top: var(--space-xl);
}

.module-card {
  cursor: pointer;
  position: relative;
  overflow: hidden;
}

.module-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.module-card:hover::before { opacity: 1; }

.module-card .module-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  background: var(--primary-light);
  color: var(--primary);
  border-radius: var(--radius-sm);
  font-weight: 700;
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-md);
}

[data-theme="dark"] .module-card .module-number {
  background: rgba(0, 120, 212, 0.2);
  color: var(--accent);
}

.module-card h3 {
  font-size: var(--font-size-md);
  font-weight: 700;
  margin-bottom: var(--space-sm);
  color: var(--text-primary);
}

.module-card p {
  font-size: var(--font-size-sm);
  color: var(--text-tertiary);
  line-height: 1.6;
  margin-bottom: var(--space-md);
}

.module-card .module-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
}

.module-card .lesson-count {
  display: flex;
  align-items: center;
  gap: 4px;
}

.module-card .module-progress {
  width: 60px;
  height: 4px;
  background: var(--border);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.module-card .module-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: var(--radius-full);
  transition: width var(--transition-slow);
}

/* ============================================================
   LABS
   ============================================================ */
.lab-card {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin: var(--space-lg) 0;
}

.lab-card-header {
  padding: var(--space-md) var(--space-lg);
  background: linear-gradient(135deg, rgba(0, 120, 212, 0.08), rgba(80, 230, 255, 0.05));
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.lab-card-header .lab-icon {
  font-size: var(--font-size-lg);
}

.lab-card-header h4 {
  font-weight: 700;
  font-size: var(--font-size-base);
  color: var(--text-primary);
}

.lab-card-body {
  padding: var(--space-lg);
}

.lab-step {
  display: flex;
  gap: var(--space-md);
  margin-bottom: var(--space-lg);
  padding-bottom: var(--space-lg);
  border-bottom: 1px solid var(--border);
}

.lab-step:last-child {
  border-bottom: none;
  margin-bottom: 0;
  padding-bottom: 0;
}

.lab-step-number {
  flex-shrink: 0;
  width: 28px;
  height: 28px;
  background: var(--primary);
  color: white;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-xs);
  font-weight: 700;
  margin-top: 2px;
}

.lab-step-content h5 {
  font-weight: 600;
  margin-bottom: var(--space-sm);
  color: var(--text-primary);
}

.lab-step-content p {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  margin-bottom: var(--space-sm);
}

.lab-prereqs {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  margin-bottom: var(--space-md);
}

.lab-prereq-tag {
  padding: 3px 10px;
  background: var(--warning-bg);
  color: var(--warning);
  border-radius: var(--radius-full);
  font-size: var(--font-size-xs);
  font-weight: 500;
}

/* ============================================================
   QUIZ
   ============================================================ */
.quiz-container {
  margin: var(--space-2xl) 0;
  border: 2px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.quiz-header {
  padding: var(--space-md) var(--space-lg);
  background: linear-gradient(135deg, rgba(0, 120, 212, 0.1), rgba(80, 230, 255, 0.05));
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.quiz-header h3 {
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.quiz-score {
  font-size: var(--font-size-sm);
  color: var(--text-tertiary);
  font-weight: 500;
}

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

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

.quiz-question:last-child {
  border-bottom: none;
  margin-bottom: 0;
  padding-bottom: 0;
}

.quiz-question-text {
  font-weight: 600;
  margin-bottom: var(--space-md);
  font-size: var(--font-size-base);
  color: var(--text-primary);
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: var(--space-sm);
}

.quiz-option {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

.quiz-option:hover {
  border-color: var(--primary);
  background: var(--primary-light);
  color: var(--text-primary);
}

[data-theme="dark"] .quiz-option:hover {
  background: rgba(0, 120, 212, 0.15);
}

.quiz-option.selected {
  border-color: var(--primary);
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 500;
}

[data-theme="dark"] .quiz-option.selected {
  background: rgba(0, 120, 212, 0.2);
  color: var(--accent);
  border-color: var(--accent);
}

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

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

.quiz-option .option-letter {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--bg-code);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: var(--font-size-xs);
  flex-shrink: 0;
}

.quiz-explanation {
  margin-top: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  background: var(--info-bg);
  border-radius: var(--radius-sm);
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  display: none;
}

.quiz-explanation.visible {
  display: block;
  animation: fadeInUp 0.3s ease;
}

.quiz-actions {
  padding: var(--space-md) var(--space-lg);
  border-top: 1px solid var(--border);
  display: flex;
  gap: var(--space-md);
  justify-content: flex-end;
}

.quiz-result {
  padding: var(--space-lg);
  text-align: center;
  display: none;
}

.quiz-result.visible { display: block; }

.quiz-result .score-circle {
  width: 100px;
  height: 100px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto var(--space-md);
  font-size: var(--font-size-2xl);
  font-weight: 800;
  border: 4px solid;
}

.quiz-result .score-circle.pass {
  border-color: var(--success);
  color: var(--success);
  background: var(--success-bg);
}

.quiz-result .score-circle.fail {
  border-color: var(--error);
  color: var(--error);
  background: var(--error-bg);
}

/* ============================================================
   PROGRESS DASHBOARD
   ============================================================ */
.progress-dashboard {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--space-lg);
}

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

.progress-card h4 {
  font-weight: 600;
  font-size: var(--font-size-sm);
  margin-bottom: var(--space-md);
  color: var(--text-primary);
}

.progress-bar {
  height: 8px;
  background: var(--border);
  border-radius: var(--radius-full);
  overflow: hidden;
  margin-bottom: var(--space-sm);
}

.progress-bar-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: var(--radius-full);
  transition: width 0.8s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.progress-percent {
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
  text-align: right;
}

.progress-overall-card {
  grid-column: 1 / -1;
  background: var(--bg-hero);
  color: white;
  border: none;
  position: relative;
  overflow: hidden;
}

.progress-overall-card::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -20%;
  width: 200px;
  height: 200px;
  background: radial-gradient(circle, rgba(80, 230, 255, 0.2) 0%, transparent 70%);
  border-radius: 50%;
}

.progress-overall-card h4 { color: white; }
.progress-overall-card .progress-percent { color: rgba(255,255,255,0.7); }
.progress-overall-card .progress-bar { background: rgba(255,255,255,0.2); }
.progress-overall-card .progress-bar-fill { background: linear-gradient(90deg, #50E6FF, #FFB900); }

/* ============================================================
   SEARCH OVERLAY
   ============================================================ */
.search-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  z-index: 2000;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding-top: 15vh;
  backdrop-filter: blur(4px);
}

.search-overlay.active {
  display: flex;
  animation: fadeIn 0.2s ease;
}

.search-modal {
  background: var(--bg-surface);
  border-radius: var(--radius-lg);
  width: 90%;
  max-width: 640px;
  max-height: 70vh;
  overflow: hidden;
  box-shadow: var(--shadow-xl);
  display: flex;
  flex-direction: column;
  animation: slideDown 0.3s ease;
}

.search-input-wrapper {
  display: flex;
  align-items: center;
  padding: var(--space-md) var(--space-lg);
  border-bottom: 1px solid var(--border);
  gap: var(--space-sm);
}

.search-input-wrapper .search-icon {
  color: var(--text-tertiary);
  font-size: var(--font-size-lg);
  flex-shrink: 0;
}

.search-input-wrapper input {
  flex: 1;
  border: none;
  background: transparent;
  font-size: var(--font-size-lg);
  color: var(--text-primary);
  outline: none;
  font-family: var(--font-sans);
}

.search-input-wrapper input::placeholder { color: var(--text-tertiary); }

.search-input-wrapper .search-shortcut {
  padding: 2px 8px;
  background: var(--bg-code);
  border-radius: 4px;
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
  font-family: var(--font-mono);
}

.search-results {
  overflow-y: auto;
  padding: var(--space-sm);
}

.search-result-item {
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background var(--transition-fast);
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.search-result-item:hover, .search-result-item.focused {
  background: var(--primary-light);
}

[data-theme="dark"] .search-result-item:hover,
[data-theme="dark"] .search-result-item.focused {
  background: rgba(0, 120, 212, 0.15);
}

.search-result-item .result-title {
  font-weight: 600;
  font-size: var(--font-size-sm);
  color: var(--text-primary);
}

.search-result-item .result-module {
  font-size: var(--font-size-xs);
  color: var(--text-tertiary);
}

.search-result-item mark {
  background: rgba(255, 185, 0, 0.3);
  color: inherit;
  border-radius: 2px;
  padding: 0 1px;
}

.search-empty {
  padding: var(--space-2xl);
  text-align: center;
  color: var(--text-tertiary);
  font-size: var(--font-size-sm);
}

/* ============================================================
   GLOSSARY
   ============================================================ */
.glossary-search {
  position: sticky;
  top: 0;
  background: var(--bg-root);
  padding: var(--space-md) 0;
  z-index: 10;
}

.glossary-search input {
  width: 100%;
  padding: var(--space-sm) var(--space-md);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: var(--bg-surface);
  color: var(--text-primary);
  font-size: var(--font-size-base);
  font-family: var(--font-sans);
  outline: none;
  transition: border-color var(--transition-fast);
}

.glossary-search input:focus {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(0, 120, 212, 0.15);
}

.glossary-letter-group {
  margin-bottom: var(--space-xl);
}

.glossary-letter {
  font-size: var(--font-size-2xl);
  font-weight: 800;
  color: var(--primary);
  margin-bottom: var(--space-md);
  padding-bottom: var(--space-sm);
  border-bottom: 2px solid var(--border);
}

.glossary-term {
  padding: var(--space-md);
  border-radius: var(--radius-md);
  margin-bottom: var(--space-sm);
  transition: background var(--transition-fast);
}

.glossary-term:hover {
  background: var(--bg-surface-hover);
}

.glossary-term dt {
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--space-xs);
}

.glossary-term dd {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  line-height: 1.7;
}

/* ============================================================
   TROUBLESHOOTING CENTER
   ============================================================ */
.troubleshoot-card {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  margin-bottom: var(--space-md);
  overflow: hidden;
}

.troubleshoot-card-header {
  padding: var(--space-md) var(--space-lg);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: background var(--transition-fast);
}

.troubleshoot-card-header:hover {
  background: var(--bg-surface-hover);
}

.troubleshoot-card-header h4 {
  font-size: var(--font-size-sm);
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.troubleshoot-card-body {
  padding: 0 var(--space-lg) var(--space-lg);
  display: none;
}

.troubleshoot-card.open .troubleshoot-card-body {
  display: block;
  animation: fadeInUp 0.3s ease;
}

.troubleshoot-card .severity-badge {
  padding: 2px 8px;
  border-radius: var(--radius-full);
  font-size: var(--font-size-xs);
  font-weight: 600;
}

.severity-common { background: var(--info-bg); color: var(--info); }
.severity-warning { background: var(--warning-bg); color: var(--warning); }
.severity-critical { background: var(--error-bg); color: var(--error); }

/* ============================================================
   LESSON NAVIGATION (Prev/Next)
   ============================================================ */
.lesson-nav {
  display: flex;
  gap: var(--space-md);
  margin-top: var(--space-2xl);
  padding-top: var(--space-xl);
  border-top: 2px solid var(--border);
}

.lesson-nav-btn {
  flex: 1;
  padding: var(--space-lg);
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  cursor: pointer;
  transition: all var(--transition-base);
  text-align: left;
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
}

.lesson-nav-btn:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

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

.lesson-nav-btn .nav-direction {
  font-size: var(--font-size-xs);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-tertiary);
}

.lesson-nav-btn .nav-title {
  font-weight: 600;
  color: var(--text-primary);
  font-size: var(--font-size-sm);
}

/* Complete lesson button */
.complete-lesson-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  width: 100%;
  padding: var(--space-md);
  background: var(--success);
  color: white;
  border: none;
  border-radius: var(--radius-md);
  font-size: var(--font-size-base);
  font-weight: 600;
  margin-top: var(--space-lg);
  transition: all var(--transition-fast);
}

.complete-lesson-btn:hover {
  filter: brightness(1.1);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(16, 185, 129, 0.3);
}

.complete-lesson-btn.completed {
  background: var(--bg-surface);
  color: var(--success);
  border: 2px solid var(--success);
}

/* ============================================================
   SUMMARY CARD
   ============================================================ */
.summary-card {
  background: linear-gradient(135deg, rgba(0, 120, 212, 0.05), rgba(80, 230, 255, 0.03));
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  margin: var(--space-xl) 0;
}

.summary-card h3 {
  font-weight: 700;
  margin-bottom: var(--space-md);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  color: var(--text-primary);
}

.summary-card ul {
  list-style: none;
  padding: 0;
}

.summary-card li {
  padding: var(--space-xs) 0;
  padding-left: var(--space-lg);
  position: relative;
  color: var(--text-secondary);
  font-size: var(--font-size-sm);
}

.summary-card li::before {
  content: '✓';
  position: absolute;
  left: 0;
  color: var(--success);
  font-weight: 700;
}

/* ============================================================
   ROADMAP
   ============================================================ */
.roadmap {
  position: relative;
  padding-left: 40px;
}

.roadmap::before {
  content: '';
  position: absolute;
  left: 15px;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--border);
}

.roadmap-item {
  position: relative;
  margin-bottom: var(--space-xl);
  padding: var(--space-lg);
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  transition: all var(--transition-base);
}

.roadmap-item:hover {
  border-color: var(--border-hover);
  box-shadow: var(--shadow-md);
}

.roadmap-item::before {
  content: '';
  position: absolute;
  left: -33px;
  top: 24px;
  width: 14px;
  height: 14px;
  background: var(--bg-surface);
  border: 3px solid var(--primary);
  border-radius: 50%;
  z-index: 1;
}

.roadmap-item.completed::before {
  background: var(--success);
  border-color: var(--success);
}

.roadmap-item .roadmap-phase {
  font-size: var(--font-size-xs);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--primary);
  font-weight: 600;
  margin-bottom: var(--space-xs);
}

.roadmap-item h3 {
  font-weight: 700;
  margin-bottom: var(--space-sm);
}

.roadmap-item p {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

/* ============================================================
   DOWNLOAD SECTION
   ============================================================ */
.download-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: var(--space-lg);
}

.download-card {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  text-align: center;
  transition: all var(--transition-base);
  cursor: pointer;
}

.download-card:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.download-card .download-icon {
  font-size: 2rem;
  margin-bottom: var(--space-md);
}

.download-card h4 {
  font-weight: 600;
  margin-bottom: var(--space-sm);
}

.download-card p {
  font-size: var(--font-size-sm);
  color: var(--text-tertiary);
}

/* ============================================================
   ANIMATIONS
   ============================================================ */
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(16px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideDown {
  from {
    opacity: 0;
    transform: translateY(-20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

@keyframes shimmer {
  0% { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

/* Page transition */
.page-enter {
  animation: fadeInUp 0.35s ease;
}

/* Stagger children */
.stagger > * {
  opacity: 0;
  animation: fadeInUp 0.4s ease forwards;
}

.stagger > *:nth-child(1) { animation-delay: 0.05s; }
.stagger > *:nth-child(2) { animation-delay: 0.1s; }
.stagger > *:nth-child(3) { animation-delay: 0.15s; }
.stagger > *:nth-child(4) { animation-delay: 0.2s; }
.stagger > *:nth-child(5) { animation-delay: 0.25s; }
.stagger > *:nth-child(6) { animation-delay: 0.3s; }
.stagger > *:nth-child(7) { animation-delay: 0.35s; }
.stagger > *:nth-child(8) { animation-delay: 0.4s; }
.stagger > *:nth-child(9) { animation-delay: 0.45s; }
.stagger > *:nth-child(10) { animation-delay: 0.5s; }
.stagger > *:nth-child(11) { animation-delay: 0.55s; }
.stagger > *:nth-child(12) { animation-delay: 0.6s; }

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 1024px) {
  .sidebar {
    transform: translateX(-100%);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .mobile-header {
    display: flex;
  }

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

  .hero h1 {
    font-size: var(--font-size-3xl);
  }

  .hero-stats {
    gap: var(--space-lg);
  }
}

@media (max-width: 768px) {
  .page-content {
    padding: var(--space-lg) var(--space-md);
  }

  .hero {
    padding: var(--space-2xl) var(--space-lg);
  }

  .hero h1 {
    font-size: var(--font-size-2xl);
  }

  .module-grid {
    grid-template-columns: 1fr;
  }

  .lesson-nav {
    flex-direction: column;
  }

  .hero-actions {
    flex-direction: column;
  }

  .progress-dashboard {
    grid-template-columns: 1fr;
  }

  .download-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .hero-stats {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--space-md);
  }
}

/* ============================================================
   PRINT STYLES
   ============================================================ */
@media print {
  .sidebar,
  .mobile-header,
  .sidebar-overlay,
  .search-overlay,
  .theme-toggle,
  .complete-lesson-btn,
  .lesson-nav,
  .hero-actions {
    display: none !important;
  }

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

  body {
    color: #000;
    background: #fff;
    font-size: 12pt;
  }

  .hero {
    background: none !important;
    color: #000 !important;
    padding: 20px 0;
  }

  .code-block {
    border: 1px solid #ccc;
    page-break-inside: avoid;
  }

  .card, .lab-card, .quiz-container {
    border: 1px solid #ccc;
    box-shadow: none;
    page-break-inside: avoid;
  }

  a { color: #000; text-decoration: underline; }
  a::after { content: ' (' attr(href) ')'; font-size: 9pt; color: #666; }
}

/* ============================================================
   UTILITY CLASSES
   ============================================================ */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

.text-center { text-align: center; }
.text-muted { color: var(--text-tertiary); }
.mt-lg { margin-top: var(--space-lg); }
.mt-xl { margin-top: var(--space-xl); }
.mt-2xl { margin-top: var(--space-2xl); }
.mb-lg { margin-bottom: var(--space-lg); }
.mb-xl { margin-bottom: var(--space-xl); }

.flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  padding: 3px 10px;
  border-radius: var(--radius-full);
  font-size: var(--font-size-xs);
  font-weight: 500;
}

.tag-blue { background: var(--info-bg); color: var(--info); }
.tag-green { background: var(--success-bg); color: var(--success); }
.tag-yellow { background: var(--warning-bg); color: var(--warning); }
.tag-red { background: var(--error-bg); color: var(--error); }

/* Real-world importance section */
.real-world-section {
  background: linear-gradient(135deg, rgba(255, 185, 0, 0.08), rgba(255, 185, 0, 0.02));
  border: 1px solid rgba(255, 185, 0, 0.2);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  margin: var(--space-xl) 0;
}

.real-world-section h3 {
  color: var(--accent-warm);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 700;
  margin-bottom: var(--space-md);
}

.real-world-section p, .real-world-section li {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

/* Try it yourself section */
.try-it-section {
  background: linear-gradient(135deg, rgba(16, 185, 129, 0.08), rgba(16, 185, 129, 0.02));
  border: 1px solid rgba(16, 185, 129, 0.2);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  margin: var(--space-xl) 0;
}

.try-it-section h3 {
  color: var(--success);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 700;
  margin-bottom: var(--space-md);
}

.try-it-section ol, .try-it-section ul {
  padding-left: var(--space-lg);
}

.try-it-section li {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  margin-bottom: var(--space-sm);
}

/* Lesson page section anchors */
.section-anchor {
  scroll-margin-top: calc(var(--header-height) + var(--space-lg));
}

/* Tab-style content switcher */
.tab-container {
  margin: var(--space-lg) 0;
}

.tab-headers {
  display: flex;
  border-bottom: 2px solid var(--border);
  gap: 0;
}

.tab-header {
  padding: var(--space-sm) var(--space-lg);
  border: none;
  background: none;
  color: var(--text-tertiary);
  font-size: var(--font-size-sm);
  font-weight: 500;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  margin-bottom: -2px;
  transition: all var(--transition-fast);
  font-family: var(--font-sans);
}

.tab-header:hover {
  color: var(--text-primary);
}

.tab-header.active {
  color: var(--primary);
  border-bottom-color: var(--primary);
  font-weight: 600;
}

.tab-content {
  padding: var(--space-lg) 0;
}

.tab-panel {
  display: none;
}

.tab-panel.active {
  display: block;
  animation: fadeInUp 0.3s ease;
}

/* ============================================================
   AUTH OVERLAY
   ============================================================ */
.auth-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(4px);
  z-index: 2000;
  align-items: center;
  justify-content: center;
  opacity: 0;
  transition: opacity var(--transition-base);
}

.auth-overlay.active {
  display: flex;
  opacity: 1;
}

.auth-modal {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  width: 90%;
  max-width: 400px;
  padding: var(--space-xl);
  box-shadow: var(--shadow-xl);
  transform: translateY(20px);
  transition: transform var(--transition-base);
}

.auth-overlay.active .auth-modal {
  transform: translateY(0);
}

.auth-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--space-lg);
}

.auth-header h2 {
  font-size: var(--font-size-2xl);
  font-weight: 800;
  color: var(--text-primary);
}

.close-auth {
  background: none;
  border: none;
  font-size: var(--font-size-xl);
  color: var(--text-tertiary);
  cursor: pointer;
  transition: color var(--transition-fast);
}

.close-auth:hover {
  color: var(--text-primary);
}

.form-group {
  margin-bottom: var(--space-md);
}

.form-group label {
  display: block;
  font-size: var(--font-size-sm);
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: var(--space-xs);
}

.form-group input {
  width: 100%;
  padding: var(--space-sm) var(--space-md);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: var(--bg-root);
  color: var(--text-primary);
  font-size: var(--font-size-base);
  outline: none;
  transition: border-color var(--transition-fast);
}

.form-group input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(0, 120, 212, 0.15);
}

.auth-error {
  color: var(--error);
  font-size: var(--font-size-sm);
  margin-top: var(--space-sm);
  min-height: 20px;
  display: none;
}

.auth-error.visible {
  display: block;
}

.auth-toggle {
  margin-top: var(--space-lg);
  text-align: center;
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
}

.auth-sidebar-btn {
  margin-bottom: var(--space-sm);
}

.auth-mobile-btn {
  font-size: 1.2rem;
}