/* ============================================================
   How AI Actually Works — Global Styles
   Dark theme, technical precision, edutainment warmth
   ============================================================ */

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

:root {
  --bg: #0a0a0f;
  --surface: #14141f;
  --surface-hover: #1a1a2e;
  --text: #e8e8f0;
  --text-dim: #9898a8;
  --accent: #6366f1;
  --accent-light: #818cf8;
  --cyan: #22d3ee;
  --orange: #f97316;
  --green: #34d399;
  --red: #ef4444;
  --code: #a5b4fc;
  --border: #2a2a3f;
  --border-light: #3a3a5f;
  --radius: 12px;
  --radius-sm: 8px;
  --max-width: 72ch;
  --sidebar-width: 280px;
}

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

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  min-height: 100vh;
  overflow-x: hidden;
}

/* --- Typography --- */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
}

h1 { font-size: clamp(2rem, 5vw, 3.5rem); margin-bottom: 1rem; }
h2 { font-size: clamp(1.5rem, 3.5vw, 2.5rem); margin: 2.5rem 0 1rem; }
h3 { font-size: clamp(1.2rem, 2.5vw, 1.75rem); margin: 2rem 0 0.75rem; }

p { margin-bottom: 1.25rem; max-width: var(--max-width); }
p:last-child { margin-bottom: 0; }

a {
  color: var(--accent-light);
  text-decoration: underline;
  text-decoration-color: rgba(99, 102, 241, 0.3);
  text-underline-offset: 3px;
  transition: color 0.2s, text-decoration-color 0.2s;
}
a:hover {
  color: var(--cyan);
  text-decoration-color: var(--cyan);
}

strong { color: #fff; font-weight: 600; }

code, .code {
  font-family: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;
  font-size: 0.9em;
  color: var(--code);
  background: rgba(99, 102, 241, 0.1);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}

pre {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 1.25rem;
  overflow-x: auto;
  margin: 1.5rem 0;
  font-size: 0.875rem;
  line-height: 1.6;
}
pre code {
  background: none;
  padding: 0;
  font-size: inherit;
}

blockquote {
  border-left: 3px solid var(--accent);
  padding: 1rem 1.5rem;
  margin: 1.5rem 0;
  background: rgba(99, 102, 241, 0.05);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-style: italic;
  color: var(--text-dim);
}
blockquote strong, blockquote cite {
  color: var(--text);
  font-style: normal;
}

/* --- Layout --- */
.page-wrapper {
  display: flex;
  min-height: 100vh;
}

.sidebar {
  position: fixed;
  top: 0;
  left: 0;
  width: var(--sidebar-width);
  height: 100vh;
  background: var(--surface);
  border-right: 1px solid var(--border);
  padding: 2rem 1.5rem;
  overflow-y: auto;
  z-index: 100;
  transition: transform 0.3s ease;
}

.sidebar-title {
  font-size: 0.875rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  margin-bottom: 1.5rem;
}

.sidebar-title a {
  color: var(--text-dim);
  text-decoration: none;
}
.sidebar-title a:hover { color: var(--accent-light); }

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

.sidebar-nav li {
  margin-bottom: 0.25rem;
}

.sidebar-nav a {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.6rem 0.75rem;
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--text-dim);
  font-size: 0.9rem;
  transition: all 0.2s;
}

.sidebar-nav a:hover {
  background: var(--surface-hover);
  color: var(--text);
}

.sidebar-nav a.active {
  background: rgba(99, 102, 241, 0.15);
  color: var(--accent-light);
  font-weight: 500;
}

.sidebar-nav .lesson-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.5rem;
  height: 1.5rem;
  border-radius: 50%;
  background: var(--border);
  font-size: 0.75rem;
  font-weight: 600;
  flex-shrink: 0;
}

.sidebar-nav a.active .lesson-num {
  background: var(--accent);
  color: #fff;
}

.sidebar-nav a.completed .lesson-num {
  background: var(--green);
  color: var(--bg);
}

.main-content {
  margin-left: var(--sidebar-width);
  flex: 1;
  min-width: 0;
}

/* Mobile sidebar toggle */
.sidebar-toggle {
  display: none;
  position: fixed;
  top: 1rem;
  left: 1rem;
  z-index: 200;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.5rem 0.75rem;
  color: var(--text);
  cursor: pointer;
  font-size: 1.25rem;
}

/* --- Hero Section --- */
.lesson-hero {
  padding: 4rem 2rem 3rem;
  max-width: 900px;
  margin: 0 auto;
}

.lesson-meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
}

.lesson-number {
  background: var(--accent);
  color: #fff;
  font-size: 0.8rem;
  font-weight: 700;
  padding: 0.3rem 0.75rem;
  border-radius: 20px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.lesson-time {
  color: var(--text-dim);
  font-size: 0.875rem;
}

.lesson-hero h1 {
  margin-bottom: 1.5rem;
}

.learning-objectives {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-top: 1.5rem;
}

.learning-objectives h4 {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  margin-bottom: 0.75rem;
}

.learning-objectives ul {
  list-style: none;
  padding: 0;
}

.learning-objectives li {
  padding: 0.4rem 0;
  padding-left: 1.5rem;
  position: relative;
  color: var(--text-dim);
  font-size: 0.95rem;
}

.learning-objectives li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.7rem;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent);
}

/* --- Content Sections --- */
.lesson-content {
  padding: 0 2rem 4rem;
  max-width: 900px;
  margin: 0 auto;
}

.content-section {
  margin-bottom: 3rem;
}

.content-section img {
  width: 100%;
  border-radius: var(--radius);
  margin: 1.5rem 0;
}

/* --- Cards --- */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin: 1.5rem 0;
}

.card-accent {
  border-left: 3px solid var(--accent);
}

.card-cyan {
  border-left: 3px solid var(--cyan);
}

.card-orange {
  border-left: 3px solid var(--orange);
}

/* --- Stat Cards --- */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}

.stat-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  text-align: center;
}

.stat-value {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 800;
  color: var(--cyan);
  line-height: 1.1;
  margin-bottom: 0.5rem;
}

.stat-label {
  font-size: 0.85rem;
  color: var(--text-dim);
}

/* --- Tables --- */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.9rem;
}

th {
  text-align: left;
  padding: 0.75rem 1rem;
  background: var(--surface);
  border-bottom: 2px solid var(--border);
  color: var(--text-dim);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

td {
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--border);
}

tr:hover td {
  background: rgba(99, 102, 241, 0.03);
}

/* --- Key Terms --- */
.key-term {
  display: inline;
  color: var(--cyan);
  cursor: help;
  border-bottom: 1px dashed var(--cyan);
  position: relative;
}

.key-term .tooltip {
  display: none;
  position: absolute;
  bottom: calc(100% + 8px);
  left: 50%;
  transform: translateX(-50%);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  font-size: 0.85rem;
  color: var(--text);
  width: max-content;
  max-width: 300px;
  z-index: 50;
  box-shadow: 0 4px 20px rgba(0,0,0,0.4);
  font-style: normal;
  cursor: default;
}

.key-term:hover .tooltip {
  display: block;
}

/* --- "Did This Land?" Section --- */
.comprehension {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin: 3rem 0;
}

.comprehension h3 {
  color: var(--green);
  margin-top: 0;
  margin-bottom: 1.25rem;
}

.comprehension-q {
  margin-bottom: 1.5rem;
}

.comprehension-q p {
  font-weight: 500;
  color: #fff;
  margin-bottom: 0.5rem;
}

.comprehension-q .answer {
  display: none;
  padding: 0.75rem 1rem;
  background: rgba(34, 211, 238, 0.05);
  border-left: 2px solid var(--cyan);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin-top: 0.5rem;
  color: var(--text-dim);
  font-size: 0.9rem;
}

.comprehension-q .answer.show {
  display: block;
}

.reveal-btn {
  background: none;
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 0.4rem 1rem;
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
  transition: all 0.2s;
}

.reveal-btn:hover {
  border-color: var(--cyan);
  color: var(--cyan);
}

/* --- Lesson Navigation --- */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  padding: 2rem 0;
  border-top: 1px solid var(--border);
  margin-top: 3rem;
  gap: 1rem;
}

.lesson-nav a {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--text-dim);
  font-size: 0.9rem;
  transition: all 0.2s;
}

.lesson-nav a:hover {
  border-color: var(--accent);
  color: var(--accent-light);
}

.lesson-nav .next {
  margin-left: auto;
}

/* --- YouTube Embed --- */
.video-embed {
  margin: 2rem 0;
  border-radius: var(--radius);
  overflow: hidden;
  border: 1px solid var(--border);
}

.video-embed iframe {
  width: 100%;
  aspect-ratio: 16/9;
  border: none;
  display: block;
}

.video-embed .video-caption {
  padding: 0.75rem 1rem;
  background: var(--surface);
  font-size: 0.85rem;
  color: var(--text-dim);
}

/* --- Pop Culture Callout --- */
.pop-culture {
  background: linear-gradient(135deg, rgba(249, 115, 22, 0.05), rgba(99, 102, 241, 0.05));
  border: 1px solid var(--border);
  border-left: 3px solid var(--orange);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}

.pop-culture .label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--orange);
  font-weight: 600;
  margin-bottom: 0.5rem;
}

/* --- History Thread --- */
.history-thread {
  background: rgba(34, 211, 238, 0.03);
  border: 1px solid var(--border);
  border-left: 3px solid var(--cyan);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}

.history-thread .label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--cyan);
  font-weight: 600;
  margin-bottom: 0.5rem;
}

/* --- Animation Container --- */
.animation-container {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin: 2rem 0;
  min-height: 300px;
  position: relative;
  overflow: hidden;
}

.animation-label {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  background: var(--bg);
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
}

/* --- Glossary --- */
.glossary {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin: 2rem 0;
}

.glossary h3 {
  margin-top: 0;
  font-size: 1rem;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.glossary dl {
  margin: 0;
}

.glossary dt {
  color: var(--cyan);
  font-weight: 600;
  margin-top: 1rem;
}

.glossary dt:first-of-type { margin-top: 0.5rem; }

.glossary dd {
  color: var(--text-dim);
  font-size: 0.9rem;
  margin-left: 0;
  padding-left: 1rem;
  border-left: 1px solid var(--border);
  margin-top: 0.25rem;
}

/* --- Lesson Summary --- */
.lesson-summary {
  background: linear-gradient(135deg, rgba(99, 102, 241, 0.08), rgba(34, 211, 238, 0.05));
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin: 2rem 0;
}

.lesson-summary h3 {
  margin-top: 0;
  margin-bottom: 1rem;
}

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

.lesson-summary li {
  padding: 0.5rem 0;
  padding-left: 1.75rem;
  position: relative;
  color: var(--text-dim);
}

.lesson-summary li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.85rem;
  width: 10px;
  height: 2px;
  background: var(--accent);
}

/* --- Course Home Cards --- */
.lesson-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1.25rem;
  margin: 2rem 0;
}

.lesson-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.75rem;
  text-decoration: none;
  color: var(--text);
  transition: all 0.3s ease;
  display: block;
}

.lesson-card:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
  box-shadow: 0 8px 30px rgba(99, 102, 241, 0.15);
}

.lesson-card .card-num {
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--accent);
  margin-bottom: 0.5rem;
}

.lesson-card h3 {
  font-size: 1.25rem;
  margin: 0 0 0.5rem;
  color: #fff;
}

.lesson-card p {
  font-size: 0.9rem;
  color: var(--text-dim);
  margin: 0;
}

.lesson-card .card-time {
  font-size: 0.8rem;
  color: var(--text-dim);
  margin-top: 0.75rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

/* --- Responsive --- */
@media (max-width: 768px) {
  .sidebar {
    transform: translateX(-100%);
  }
  .sidebar.open {
    transform: translateX(0);
  }
  .sidebar-toggle {
    display: block;
  }
  .main-content {
    margin-left: 0;
  }
  .lesson-hero {
    padding: 3rem 1.25rem 2rem;
  }
  .lesson-content {
    padding: 0 1.25rem 3rem;
  }
  .stat-grid {
    grid-template-columns: 1fr 1fr;
  }
  .lesson-grid {
    grid-template-columns: 1fr;
  }
  .lesson-nav {
    flex-direction: column;
  }
}

@media (max-width: 480px) {
  .stat-grid {
    grid-template-columns: 1fr;
  }
}

/* --- Reduced Motion --- */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
  html { scroll-behavior: auto; }
}

/* --- Print --- */
@media print {
  .sidebar, .sidebar-toggle, .lesson-nav { display: none; }
  .main-content { margin-left: 0; }
  body { background: #fff; color: #000; }
  .card, .stat-card, .comprehension, .animation-container {
    border-color: #ccc;
    background: #f9f9f9;
  }
}