/* ============================================
   AI in Education — Design System
   University of Dhaka | Dark Glassmorphism Theme
   ============================================ */

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

/* ---------- CSS Custom Properties ---------- */
:root {
  /* Colors */
  --bg-primary: #ffffff;
  --bg-secondary: #fafafa;
  --bg-card: #ffffff;
  --bg-glass: #ffffff;
  --bg-glass-hover: #f4f4f5;
  --border-glass: #e5e7eb;
  --border-glass-hover: #d4d4d8;

  --text-primary: #0a0a0a;
  --text-secondary: #52525b;
  --text-muted: #71717a;

  /* Accents (use sparingly) */
  --accent-1: #0a0a0a;
  --accent-2: #111827;
  --accent-3: #2563eb;
  --accent-4: #0a0a0a;
  --accent-5: #0a0a0a;
  --accent-6: #0a0a0a;
  --accent-7: #0a0a0a;
  --accent-8: #0a0a0a;

  --gradient-hero: #0a0a0a;
  --gradient-l1: #0a0a0a;
  --gradient-l2: #0a0a0a;
  --gradient-l3: #0a0a0a;
  --gradient-l4: #0a0a0a;
  --gradient-l5: #0a0a0a;

  /* Typography */
  --font-heading: 'Geist', sans-serif;
  --font-body: 'Geist', sans-serif;
  --font-mono: 'Geist Mono', ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;
  --space-4xl: 6rem;

  /* Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-xl: 18px;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 6px 20px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 18px 45px rgba(0, 0, 0, 0.12);
  --shadow-glow: 0 0 0 rgba(0, 0, 0, 0);

  /* Transitions */
  --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);

  /* Layout */
  --max-width: 1120px;
  --nav-height: 72px;
}

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

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-body);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
  min-height: 100vh;
}

a {
  color: var(--accent-3);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--accent-4);
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

ul, ol {
  padding-left: var(--space-lg);
}

li {
  margin-bottom: var(--space-sm);
}

/* ---------- Typography ---------- */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: 700;
  line-height: 1.2;
  color: var(--text-primary);
}

h1 { font-size: clamp(2rem, 5vw, 3.5rem); font-weight: 900; }
h2 { font-size: clamp(1.5rem, 3.5vw, 2.25rem); font-weight: 800; }
h3 { font-size: clamp(1.2rem, 2.5vw, 1.5rem); font-weight: 700; }
h4 { font-size: 1.125rem; font-weight: 600; }

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

.text-gradient {
  color: var(--text-primary);
}

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

.text-gradient-l1 { background: var(--gradient-l1); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.text-gradient-l2 { background: var(--gradient-l2); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.text-gradient-l3 { background: var(--gradient-l3); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.text-gradient-l4 { background: var(--gradient-l4); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.text-gradient-l5 { background: var(--gradient-l5); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }

.text-gradient-l1,
.text-gradient-l2,
.text-gradient-l3,
.text-gradient-l4,
.text-gradient-l5 {
  color: var(--text-primary);
  -webkit-text-fill-color: initial;
}

/* ---------- Layout ---------- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-xl);
}

.section {
  padding: var(--space-4xl) 0;
  position: relative;
  z-index: 1;
}

.section-header {
  text-align: left;
  margin-bottom: var(--space-3xl);
}

.section-header p {
  max-width: 680px;
  margin: var(--space-md) 0 0;
}

.link-inline {
  color: var(--text-primary);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
}

.link-inline:hover {
  color: var(--accent-3);
}

/* ---------- Navigation ---------- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-glass);
  z-index: 1000;
  display: flex;
  align-items: center;
}

.nav .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 1.25rem;
  color: var(--text-primary);
  text-decoration: none;
}

.nav-logo .logo-icon {
  width: 28px;
  height: 28px;
  border-radius: 6px;
  background: transparent;
  display: block;
  object-fit: contain;
  border: 1px solid var(--border-glass);
  padding: 2px;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
  list-style: none;
  padding: 0;
}

.nav-links a {
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  transition: all var(--transition-fast);
  text-decoration: none;
  white-space: nowrap;
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--text-primary);
  background: var(--bg-secondary);
}

.nav-links a.active {
  color: var(--text-primary);
}

/* Hamburger */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  background: none;
  border: none;
  padding: var(--space-sm);
}

.nav-toggle span {
  width: 24px;
  height: 2px;
  background: var(--text-primary);
  border-radius: 2px;
  transition: all var(--transition-fast);
}

/* ---------- Hero Section ---------- */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: left;
  padding: calc(var(--nav-height) + var(--space-3xl)) var(--space-xl) var(--space-3xl);
  position: relative;
  overflow: hidden;
}

.hero-content {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: var(--space-3xl);
  align-items: center;
  width: 100%;
}

.hero-text {
  max-width: 560px;
}

.hero-media {
  display: flex;
  justify-content: flex-end;
}

.hero::before { content: none; }

@keyframes pulseGlow {
  0%, 100% { opacity: 0.5; transform: translateX(-50%) scale(1); }
  50% { opacity: 1; transform: translateX(-50%) scale(1.1); }
}

.hero-content {
  max-width: 800px;
  z-index: 1;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  background: var(--bg-glass);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-xl);
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
}

.hero-badge .dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent-5);
  animation: blink 2s ease-in-out infinite;
}

@keyframes blink {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.3; }
}

.hero h1 {
  margin-bottom: var(--space-lg);
  letter-spacing: -0.02em;
}

.hero .subtitle {
  font-size: clamp(1.1rem, 2.5vw, 1.35rem);
  color: var(--text-secondary);
  max-width: 680px;
  margin: 0 0 var(--space-2xl);
  line-height: 1.6;
}

.hero-cta {
  display: flex;
  gap: var(--space-md);
  justify-content: flex-start;
  flex-wrap: wrap;
  margin-bottom: var(--space-3xl);
}

.hero-image-wrapper {
  max-width: 1000px;
  margin: 0;
  border-radius: var(--radius-xl);
  overflow: hidden;
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--border-glass);
  transform: translateY(0);
  transition: transform var(--transition-slow), box-shadow var(--transition-slow);
}

.hero-image-wrapper:hover {
  transform: translateY(-10px);
  box-shadow: var(--shadow-lg);
}

.hero-image {
  width: 100%;
  height: auto;
  display: block;
  object-fit: cover;
  transition: transform 0.7s ease;
}

.hero-image-wrapper:hover .hero-image {
  transform: scale(1.02);
}

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 14px 28px;
  border-radius: var(--radius-full);
  font-family: var(--font-body);
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  border: none;
  text-decoration: none;
  transition: all var(--transition-base);
}

.btn-small {
  padding: 10px 18px;
  font-size: 0.85rem;
}

.btn-primary {
  background: var(--text-primary);
  color: #ffffff;
  box-shadow: var(--shadow-sm);
}

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

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

.btn-secondary:hover {
  background: var(--bg-glass-hover);
  border-color: var(--border-glass-hover);
  transform: translateY(-2px);
  color: var(--text-primary);
}

/* ---------- Cards ---------- */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: var(--space-xl);
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

.card::before {
  content: none;
}

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

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

.card-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  border-radius: var(--radius-md);
  background: var(--text-primary);
  font-family: var(--font-heading);
  font-weight: 800;
  font-size: 1.25rem;
  color: #ffffff;
  margin-bottom: var(--space-lg);
}

.card h3 {
  margin-bottom: var(--space-sm);
}

.card p {
  font-size: 0.95rem;
  margin-bottom: var(--space-lg);
}

.card-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  font-weight: 600;
  font-size: 0.9rem;
  color: var(--text-primary);
  transition: gap var(--transition-fast);
}

.card-link:hover {
  gap: var(--space-sm);
}

.card-link .arrow {
  transition: transform var(--transition-fast);
}

.card-link:hover .arrow {
  transform: translateX(4px);
}

.card-meta {
  display: flex;
  gap: var(--space-sm);
  margin: var(--space-md) 0 var(--space-lg);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

.card-meta span {
  padding: 4px 8px;
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  background: var(--bg-secondary);
}

/* ---------- Timeline Strip ---------- */
.timeline-strip {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: var(--space-lg);
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-3xl);
  box-shadow: var(--shadow-sm);
}

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

.timeline-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.timeline-value {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
}

.timeline-value a {
  color: var(--text-primary);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
}

.timeline-value a:hover {
  color: var(--accent-3);
}

/* ---------- About Section ---------- */
.about-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: var(--space-3xl);
  align-items: start;
}

.about-summary h3 {
  margin-bottom: var(--space-md);
}

.about-stats {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-lg);
}

.stat-item {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  box-shadow: var(--shadow-sm);
}

.stat-value {
  font-family: var(--font-mono);
  font-size: 1.6rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-xs);
  font-variant-numeric: tabular-nums;
}

.stat-label {
  color: var(--text-secondary);
  font-size: 0.9rem;
}

/* ---------- Learning Outcomes ---------- */
.outcomes-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-xl);
}

.outcome-card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: var(--space-xl);
  box-shadow: var(--shadow-sm);
}

.outcome-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-sm);
}

.outcome-card h3 {
  margin-bottom: var(--space-sm);
}

/* ---------- Course Details ---------- */
.course-details {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: var(--space-lg);
  margin-bottom: var(--space-3xl);
}

.detail-card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  box-shadow: var(--shadow-sm);
}

.detail-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-sm);
}

.detail-value {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-xs);
}

.detail-meta {
  color: var(--text-secondary);
  font-size: 0.9rem;
}

/* ---------- Instructor Section ---------- */
.instructor-card {
  display: grid;
  grid-template-columns: 180px 1fr;
  gap: var(--space-2xl);
  align-items: center;
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: var(--space-2xl);
  box-shadow: var(--shadow-sm);
}

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

.instructor-avatar {
  width: 180px;
  height: 180px;
  object-fit: cover;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-glass);
  box-shadow: var(--shadow-sm);
}

.instructor-meta {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-sm);
}

.instructor-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  margin: var(--space-md) 0 var(--space-lg);
}

.instructor-tags .lecture-tag {
  font-size: 0.75rem;
}

.instructor-title {
  color: var(--text-secondary);
  font-size: 1rem;
  margin-bottom: var(--space-md);
}

.instructor-bio {
  color: var(--text-secondary);
  margin-bottom: var(--space-lg);
}

.instructor-highlights {
  list-style: none;
  padding-left: 0;
  margin: 0 0 var(--space-lg);
  color: var(--text-secondary);
  display: grid;
  gap: var(--space-md);
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.instructor-highlights li {
  position: relative;
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: var(--space-md) var(--space-lg);
  padding-left: calc(var(--space-lg) + 18px);
}

.instructor-highlights li::before {
  content: "✓";
  position: absolute;
  left: var(--space-lg);
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-primary);
}

.instructor-links {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
}

/* Lecture-specific card accents */
.card[data-lecture="1"] { --card-accent: var(--gradient-l1); }
.card[data-lecture="2"] { --card-accent: var(--gradient-l2); }
.card[data-lecture="3"] { --card-accent: var(--gradient-l3); }
.card[data-lecture="4"] { --card-accent: var(--gradient-l4); }
.card[data-lecture="5"] { --card-accent: var(--gradient-l5); }

/* ---------- Info Grid ---------- */
.info-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: var(--space-lg);
}

.info-card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: var(--space-xl);
  display: flex;
  gap: var(--space-md);
  align-items: flex-start;
  transition: all var(--transition-base);
}

.info-card:hover {
  border-color: var(--border-glass-hover);
  background: var(--bg-glass-hover);
}

.info-icon {
  font-size: 1.5rem;
  flex-shrink: 0;
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  background: var(--bg-secondary);
}

.info-card h4 {
  margin-bottom: var(--space-xs);
}

.info-card p {
  font-size: 0.9rem;
  margin-bottom: 0;
}

/* ---------- Quote / Philosophy ---------- */
.quote-section {
  text-align: center;
  padding: var(--space-4xl) 0;
}

.quote-block {
  max-width: 700px;
  margin: 0 auto;
  padding: var(--space-2xl);
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-xl);
  backdrop-filter: none;
  position: relative;
}

.quote-block::before {
  content: '"';
  font-family: var(--font-heading);
  font-size: 6rem;
  font-weight: 900;
  position: absolute;
  top: -20px;
  left: 30px;
  color: var(--text-muted);
  opacity: 0.3;
  line-height: 1;
}

.quote-block blockquote {
  font-size: 1.15rem;
  color: var(--text-primary);
  line-height: 1.8;
  font-style: italic;
}

.quote-block cite {
  display: block;
  margin-top: var(--space-lg);
  font-size: 0.9rem;
  color: var(--text-muted);
  font-style: normal;
}

/* ---------- Lecture Page Styles ---------- */
.lecture-hero {
  padding: calc(var(--nav-height) + var(--space-3xl)) 0 var(--space-3xl);
  position: relative;
  z-index: 1;
}

.lecture-hero .container {
  max-width: 900px;
}

.lecture-meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
}

.lecture-tag {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  padding: 6px 14px;
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  font-size: 0.8rem;
  color: var(--text-secondary);
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
}

.lecture-tag .tag-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
}

.lecture-hero h1 {
  margin-bottom: var(--space-md);
}

.lecture-hero .lecture-description {
  font-size: 1.1rem;
  color: var(--text-secondary);
  max-width: 700px;
  line-height: 1.7;
}

/* Inspiration Badge */
.inspiration-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  color: var(--text-secondary);
  margin-bottom: var(--space-xl);
}

.inspiration-badge strong {
  color: var(--text-primary);
}

.lecture-banner {
  margin: var(--space-2xl) auto 0;
  max-width: 1000px;
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-glass);
}

.lecture-banner img {
  width: 100%;
  height: auto;
  display: block;
  object-fit: cover;
}

/* Content Sections */
.lecture-content {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 var(--space-xl);
}

.content-block {
  margin-bottom: var(--space-3xl);
}

.content-block-header {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
}

.content-block-icon {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  flex-shrink: 0;
}

.content-block-header h2 {
  font-size: 1.5rem;
}

.content-card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-lg);
  transition: all var(--transition-base);
}

.content-card:hover {
  border-color: var(--border-glass-hover);
  box-shadow: var(--shadow-sm);
}

.content-card h4 {
  margin-bottom: var(--space-sm);
}

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

.content-card ul li {
  padding: var(--space-sm) 0;
  padding-left: var(--space-lg);
  position: relative;
  color: var(--text-secondary);
  font-size: 0.95rem;
}

.content-card ul li::before {
  content: '→';
  position: absolute;
  left: 0;
  color: var(--accent-3);
  font-weight: 600;
}

/* ---------- Presentation UI ---------- */
.presentation-slide {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-xl);
  padding: var(--space-3xl);
  margin-bottom: var(--space-2xl);
  box-shadow: var(--shadow-sm);
  font-size: 1.05rem;
  line-height: 1.8;
  position: relative;
  overflow: hidden;
}

.presentation-slide::before {
  content: '';
  position: absolute;
  top: 0; left: 0;
  width: 4px; height: 100%;
  background: var(--text-primary);
}

/* =========================================
   PROFESSOR UPGRADES (UX/UI)
   ========================================= */

/* 1. Prompt Box with Copy Button */
.prompt-box {
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: 8px;
  padding: 1.5rem;
  margin: 1rem 0;
  position: relative;
  font-family: var(--font-mono);
  font-size: 0.95rem;
  line-height: 1.5;
  color: var(--text-primary);
}

.copy-btn {
  position: absolute;
  top: 0.5rem;
  right: 0.5rem;
  background: var(--text-primary);
  color: #ffffff;
  border: none;
  border-radius: 4px;
  padding: 0.4rem 0.8rem;
  font-size: 0.8rem;
  cursor: pointer;
  transition: all 0.2s ease;
  font-family: var(--font-body);
  font-weight: 500;
}

.copy-btn:hover {
  background: #111827;
  transform: translateY(-2px);
}

.copy-btn.copied {
  background: #16a34a;
}

/* 2. Floating Action Buttons (FAB) */
.fab-container {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  z-index: 90;
}

.fab {
  width: 50px;
  height: 50px;
  border-radius: 50%;
  background: var(--text-primary);
  border: 1px solid var(--border-glass);
  color: #ffffff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  cursor: pointer;
  box-shadow: var(--shadow-md);
  transition: all 0.3s ease;
  text-decoration: none;
}

.fab:hover {
  transform: scale(1.1);
  background: #111827;
}

.fab-glossary {
  left: 2rem;
  right: auto;
  bottom: 2rem;
  position: fixed;
  z-index: 90;
  background: var(--text-primary);
  border-color: var(--border-glass);
}

.fab-glossary:hover {
  background: #111827;
}

#fab-top {
  opacity: 0;
  pointer-events: none;
  transform: translateY(20px);
}

#fab-top.visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}

/* 3. Glossary Drawer */
.glossary-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.4);
  z-index: 99;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s ease;
}

.glossary-overlay.active {
  opacity: 1;
  pointer-events: auto;
}

.glossary-drawer {
  position: fixed;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 70vh;
  background: var(--bg-card);
  border-top: 1px solid var(--border-glass);
  border-radius: 20px 20px 0 0;
  z-index: 100;
  transform: translateY(100%);
  transition: transform 0.4s cubic-bezier(0.16, 1, 0.3, 1);
  display: flex;
  flex-direction: column;
}

.glossary-drawer.active {
  transform: translateY(0);
}

.glossary-header {
  padding: 1.5rem;
  border-bottom: 1px solid var(--border-glass);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.glossary-header h3 {
  margin: 0;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.close-glossary {
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  cursor: pointer;
}

.glossary-content {
  padding: 1.5rem;
  overflow-y: auto;
  flex: 1;
}

.glossary-term {
  margin-bottom: 1.5rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid rgba(255,255,255,0.05);
}

.glossary-term h4 {
  color: var(--text-primary);
  margin-bottom: 0.5rem;
  font-size: 1.1rem;
}

.glossary-term .bangla {
  font-size: 0.9rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
  font-style: italic;
}

.glossary-term p {
  font-size: 0.95rem;
  line-height: 1.5;
  color: var(--text-secondary);
}

@media (min-width: 768px) {
  .glossary-drawer {
    width: 400px;
    height: 100vh;
    left: 0;
    top: 0;
    bottom: auto;
    border-radius: 0;
    border-right: 1px solid rgba(255,255,255,0.1);
    transform: translateX(-100%);
  }
  .glossary-drawer.active {
    transform: translateX(0);
  }
}

.presentation-slide.slide-alt::before { background: var(--accent-4); }
.presentation-slide.slide-accent::before { background: var(--accent-8); }

.presentation-slide h3 {
  font-size: 2.2rem;
  margin-bottom: var(--space-lg);
  color: var(--text-primary);
}

.presentation-slide h4 {
  font-size: 1.5rem;
  margin-top: var(--space-xl);
  margin-bottom: var(--space-md);
  color: var(--accent-3);
}

.slide-stat-container {
  display: flex;
  gap: var(--space-xl);
  margin: var(--space-xl) 0;
  flex-wrap: wrap;
}

.slide-stat {
  flex: 1;
  min-width: 200px;
  background: var(--bg-secondary);
  padding: var(--space-xl);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-glass);
  text-align: center;
}

.slide-stat-number {
  font-size: 3.5rem;
  font-weight: 900;
  color: var(--text-primary);
  line-height: 1.1;
  margin-bottom: var(--space-sm);
  font-family: var(--font-heading);
  font-variant-numeric: tabular-nums;
}

.slide-stat-label {
  font-size: 1.1rem;
  color: var(--text-secondary);
  font-weight: 500;
}

.presentation-quote {
  font-size: 1.4rem;
  font-style: italic;
  border-left: 3px solid var(--text-primary);
  padding-left: var(--space-lg);
  margin: var(--space-xl) 0;
  color: var(--text-primary);
}

.presentation-source {
  font-size: 0.9rem;
  color: var(--text-muted);
  text-align: right;
  display: block;
  margin-top: var(--space-sm);
}

/* ---------- Stepper Progress ---------- */
.lecture-stepper {
  display: flex;
  justify-content: space-between;
  margin: var(--space-3xl) 0;
  position: relative;
  max-width: 800px;
  margin-left: auto;
  margin-right: auto;
}

.lecture-stepper::before {
  content: '';
  position: absolute;
  top: 24px;
  left: 5%;
  right: 5%;
  height: 2px;
  background: var(--border-glass);
  z-index: 0;
}

.stepper-step {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-sm);
  z-index: 1;
  position: relative;
  flex: 1;
  cursor: pointer;
}

.stepper-icon {
  width: 50px;
  height: 50px;
  border-radius: 50%;
  background: var(--bg-primary);
  border: 2px solid var(--border-glass);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  transition: all var(--transition-base);
}

.stepper-step.active .stepper-icon {
  border-color: var(--text-primary);
  box-shadow: none;
  background: var(--bg-secondary);
}

.stepper-label {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-secondary);
  text-align: center;
  transition: color var(--transition-fast);
}

.stepper-step.active .stepper-label {
  color: var(--text-primary);
}

.stepper-step:hover .stepper-icon {
  border-color: var(--text-primary);
}

.stepper-step:hover .stepper-label {
  color: var(--text-primary);
}

/* Activity cards */
.activity-card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin-bottom: var(--space-lg);
  border-left: 3px solid;
}

.activity-card.activity-1 { border-left-color: var(--accent-1); }
.activity-card.activity-2 { border-left-color: var(--accent-4); }
.activity-card.activity-3 { border-left-color: var(--accent-8); }
.activity-card.activity-4 { border-left-color: var(--accent-6); }

.activity-card h4 {
  margin-bottom: var(--space-sm);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.activity-card p {
  font-size: 0.95rem;
}

/* Takeaway Box */
.takeaway-box {
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-xl);
  padding: var(--space-2xl);
  text-align: center;
  margin-top: var(--space-2xl);
}

.takeaway-box .takeaway-icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-md);
}

.takeaway-box h3 {
  margin-bottom: var(--space-sm);
}

.takeaway-box p {
  max-width: 500px;
  margin: 0 auto;
  font-size: 0.95rem;
}

/* Resource Links */
.resource-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  margin-top: var(--space-xl);
}

.resource-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-full);
  font-size: 0.85rem;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}

.resource-link:hover {
  border-color: var(--accent-3);
  color: var(--text-primary);
  background: var(--bg-glass-hover);
}

/* Lecture Nav (Prev / Next) */
.lecture-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-lg);
  padding: var(--space-3xl) 0;
  border-top: 1px solid var(--border-glass);
  margin-top: var(--space-3xl);
}

.lecture-nav a {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
  padding: var(--space-xl);
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  transition: all var(--transition-base);
  text-decoration: none;
}

.lecture-nav a:hover {
  border-color: var(--border-glass-hover);
  background: var(--bg-glass-hover);
  transform: translateY(-2px);
}

.lecture-nav .nav-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.lecture-nav .nav-title {
  font-family: var(--font-heading);
  font-weight: 600;
  color: var(--text-primary);
}

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

/* ---------- Tools Section ---------- */
.tools-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--space-lg);
}

.tool-card {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  padding: var(--space-xl);
  text-align: center;
  transition: all var(--transition-base);
}

.tool-card:hover {
  transform: translateY(-4px);
  border-color: var(--border-glass-hover);
  box-shadow: var(--shadow-sm);
}

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

.tool-card h4 {
  margin-bottom: var(--space-xs);
}

.tool-card p {
  font-size: 0.85rem;
  margin-bottom: 0;
}

/* ---------- Footer ---------- */
.footer {
  border-top: 1px solid var(--border-glass);
  padding: var(--space-3xl) 0 var(--space-xl);
  position: relative;
  z-index: 1;
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--space-lg);
}

.footer-logo {
  font-family: var(--font-heading);
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.footer-logo .logo-icon {
  width: 22px;
  height: 22px;
  border-radius: 5px;
  object-fit: contain;
  border: 1px solid var(--border-glass);
  padding: 2px;
}

.footer-text {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin: 0;
}

.footer-links {
  display: flex;
  gap: var(--space-lg);
  list-style: none;
  padding: 0;
}

.footer-links a {
  font-size: 0.85rem;
  color: var(--text-muted);
  transition: color var(--transition-fast);
}

.footer-links a:hover {
  color: var(--text-primary);
}

/* ---------- Scroll Reveal ---------- */
.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.reveal.revealed {
  opacity: 1;
  transform: translateY(0);
}

/* ---------- Progress Bar ---------- */
.progress-bar {
  position: fixed;
  top: var(--nav-height);
  left: 0;
  height: 3px;
  background: var(--text-primary);
  z-index: 999;
  transition: width 0.1s linear;
}

/* ---------- Video Embeds ---------- */
.video-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-xl);
}

.video-grid .video-wrapper {
  margin: 0;
}

.video-wrapper {
  position: relative;
  padding-bottom: 56.25%; /* 16:9 Aspect Ratio */
  height: 0;
  overflow: hidden;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-glass);
  box-shadow: var(--shadow-sm);
  margin: var(--space-xl) 0;
  background: var(--bg-secondary);
}

.video-wrapper iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border: 0;
}

/* ---------- Accordion ---------- */
.accordion {
  margin-top: var(--space-xl);
}

.accordion-item {
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-md);
  margin-bottom: var(--space-sm);
  overflow: hidden;
}

.accordion-header {
  padding: var(--space-md) var(--space-lg);
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
  font-weight: 600;
  color: var(--text-primary);
  background: var(--bg-secondary);
  transition: background var(--transition-fast);
}

.accordion-header:hover {
  background: var(--bg-glass-hover);
}

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

.accordion-item.active .accordion-icon {
  transform: rotate(45deg);
}

.accordion-body {
  padding: 0 var(--space-lg);
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-base), padding var(--transition-base);
  color: var(--text-secondary);
}

.accordion-item.active .accordion-body {
  padding: var(--space-md) var(--space-lg);
  max-height: 1000px; /* arbitrary max for transition */
}

/* ---------- Setup Location Callout ---------- */
.setup-callout {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-lg);
  padding: var(--space-lg);
  background: var(--bg-secondary);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  margin-top: var(--space-md);
  margin-bottom: var(--space-md);
}

.setup-callout-icon {
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  flex-shrink: 0;
}

.setup-callout-title {
  font-weight: 700;
  color: var(--text-primary);
}

.setup-callout-meta {
  margin-top: var(--space-xs);
  font-size: 0.9rem;
  color: var(--text-secondary);
}

/* ---------- Responsive ---------- */
@media (max-width: 768px) {
  :root {
    --nav-height: 64px;
  }

  .nav-links {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(12px);
    flex-direction: column;
    padding: var(--space-lg);
    border-bottom: 1px solid var(--border-glass);
  }

  .nav-links.active {
    display: flex;
  }

  .nav-toggle {
    display: flex;
  }

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

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

  .tools-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .hero {
    padding-left: var(--space-lg);
    padding-right: var(--space-lg);
  }

  .hero-content {
    grid-template-columns: 1fr;
    gap: var(--space-2xl);
  }

  .hero-media {
    justify-content: flex-start;
  }

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

  .course-details {
    grid-template-columns: 1fr 1fr;
  }

  .timeline-strip {
    grid-template-columns: 1fr 1fr;
  }

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

  .instructor-card {
    grid-template-columns: 1fr;
  }

  .instructor-highlights {
    grid-template-columns: 1fr;
  }

  .setup-callout {
    flex-direction: column;
    align-items: flex-start;
  }

  .instructor-avatar {
    width: 160px;
    height: 160px;
  }

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

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

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

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

  .hero-cta {
    flex-direction: column;
    align-items: flex-start;
  }

  .resource-links {
    flex-direction: column;
  }

  .course-details {
    grid-template-columns: 1fr;
  }
}

/* ---------- Classroom Setup Table ---------- */
.setup-table {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0;
  background: var(--bg-card);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-lg);
  overflow: hidden;
  margin-top: var(--space-xl);
}

.setup-table th,
.setup-table td {
  padding: var(--space-md) var(--space-lg);
  text-align: left;
  border-bottom: 1px solid var(--border-glass);
}

.setup-table th {
  background: var(--bg-secondary);
  font-family: var(--font-heading);
  font-weight: 600;
  color: var(--text-primary);
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.setup-table td {
  font-size: 0.95rem;
  color: var(--text-secondary);
}

.setup-table tr:last-child td {
  border-bottom: none;
}

.setup-table td:first-child {
  font-weight: 600;
  color: var(--text-primary);
  white-space: nowrap;
}

/* ---------- Floating Particles (decorative) ---------- */
.particles {
  display: none;
}

.particle {
  position: absolute;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: rgba(99, 102, 241, 0.3);
  animation: float linear infinite;
}

@keyframes float {
  0% {
    transform: translateY(100vh) rotate(0deg);
    opacity: 0;
  }
  10% {
    opacity: 1;
  }
  90% {
    opacity: 1;
  }
  100% {
    transform: translateY(-100px) rotate(720deg);
    opacity: 0;
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

a:focus-visible,
button:focus-visible,
.btn:focus-visible,
.nav-toggle:focus-visible {
  outline: 2px solid var(--accent-3);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}