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

/* ── Design Tokens ── */
:root {
  --bg-base:        #020617;
  --bg-surface:     #0f172a;
  --bg-card:        rgba(15,23,42,0.4);
  --bg-input:       rgba(30,41,59,0.5);
  --border:         rgba(255,255,255,0.06);
  --border-mid:     rgba(255,255,255,0.10);
  --text-primary:   #f8fafc;
  --text-secondary: #94a3b8;
  --text-muted:     #475569;
  --accent-blue:    #2563eb;
  --accent-blue-lt: #3b82f6;
  --accent-green:   #10b981;
  --accent-teal:    #06b6d4;
  --accent-amber:   #f59e0b;
  --font-sans: 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', monospace;
  /* aliases for chapter helper functions */
  --color-text-primary:   #f8fafc;
  --color-text-secondary: #94a3b8;
  --color-text-muted:     #475569;
  --color-border: rgba(255,255,255,0.06);
  --bg-secondary: #0f172a;
  --bg-tertiary:  rgba(30,41,59,0.5);
  --bg-hover:     rgba(255,255,255,0.05);
  --font-display: 'Inter', sans-serif;
  --radius: 12px;
  --radius-lg: 20px;
}

*,*::before,*::after { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  background: var(--bg-base);
  color: var(--text-primary);
  font-size: 15px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ══════════════════════════════════════════════
   LANDING PAGE
══════════════════════════════════════════════ */

#landing-page { display: block; }
#classroom-page { display: none; }

/* Navbar */
.nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  backdrop-filter: blur(20px);
  background: rgba(2,6,23,0.8);
  border-bottom: 1px solid var(--border);
  padding: 0 24px;
}
.nav-inner {
  max-width: 1200px; margin: 0 auto;
  display: flex; align-items: center; justify-content: space-between;
  height: 64px;
}
.nav-brand {
  display: flex; align-items: center; gap: 12px;
  text-decoration: none;
}
.nav-logo {
  width: 36px; height: 36px;
  background: linear-gradient(135deg, #2563eb, #4f46e5);
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  font-weight: 800; font-size: 14px; color: #fff;
  box-shadow: 0 4px 14px rgba(37,99,235,0.35);
}
.nav-name {
  font-size: 18px; font-weight: 700; color: var(--text-primary); letter-spacing: -0.3px;
}
.nav-name span { color: #3b82f6; font-weight: 400; opacity: 0.6; }
.nav-cta {
  display: flex; align-items: center; gap: 8px;
  background: #2563eb; color: #fff;
  padding: 9px 22px; border-radius: 12px;
  font-size: 14px; font-weight: 600; border: none; cursor: pointer;
  box-shadow: 0 4px 14px rgba(37,99,235,0.35);
  transition: all 0.2s;
}
.nav-cta:hover { background: #3b82f6; transform: translateY(-1px); }

/* Hero */
.hero {
  min-height: 100vh;
  display: flex; align-items: center; justify-content: center;
  text-align: center;
  padding: 120px 24px 80px;
  position: relative; overflow: hidden;
}
.hero-glow-1 {
  position: absolute; top: -10%; left: -10%;
  width: 50%; height: 50%;
  background: radial-gradient(circle, rgba(37,99,235,0.12) 0%, transparent 70%);
  pointer-events: none;
}
.hero-glow-2 {
  position: absolute; bottom: -10%; right: -10%;
  width: 50%; height: 50%;
  background: radial-gradient(circle, rgba(79,70,229,0.10) 0%, transparent 70%);
  pointer-events: none;
}
.hero-inner { position: relative; z-index: 1; max-width: 860px; margin: 0 auto; }
.hero-badge {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 6px 18px; border-radius: 99px;
  background: rgba(16,185,129,0.1); border: 1px solid rgba(16,185,129,0.25);
  color: #10b981; font-size: 10px; font-weight: 700;
  letter-spacing: 1.5px; text-transform: uppercase;
  margin-bottom: 28px;
}
.hero-badge-dot {
  width: 7px; height: 7px; border-radius: 50%;
  background: #10b981; animation: pulse 2s infinite;
}
@keyframes pulse { 0%,100%{opacity:1;transform:scale(1)} 50%{opacity:0.5;transform:scale(1.3)} }

.hero h1 {
  font-size: clamp(40px, 7vw, 72px);
  font-weight: 800; letter-spacing: -2px; line-height: 1.05;
  background: linear-gradient(135deg, #fff 0%, rgba(248,250,252,0.6) 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  margin-bottom: 12px;
}
.hero h1 em {
  display: block;
  font-style: normal; font-size: 0.6em; font-weight: 400;
  color: #3b82f6; -webkit-text-fill-color: #3b82f6;
  opacity: 0.85; margin-top: 6px;
}
.hero-sub {
  font-size: 18px; color: var(--text-secondary); line-height: 1.7;
  max-width: 600px; margin: 20px auto 36px; font-weight: 300;
}
.hero-sub strong { color: var(--text-primary); font-weight: 500; }
.hero-cta {
  display: inline-flex; align-items: center; gap: 10px;
  background: #2563eb; color: #fff;
  padding: 16px 36px; border-radius: 16px;
  font-size: 16px; font-weight: 700; border: none; cursor: pointer;
  box-shadow: 0 8px 28px rgba(37,99,235,0.4);
  transition: all 0.2s; letter-spacing: -0.2px;
}
.hero-cta:hover { background: #3b82f6; transform: translateY(-2px); box-shadow: 0 12px 36px rgba(37,99,235,0.5); }
.hero-cta svg { transition: transform 0.2s; }
.hero-cta:hover svg { transform: translateX(4px); }

/* Info cards row */
.hero-cards {
  display: grid; grid-template-columns: 1fr 1fr;
  gap: 20px; margin-top: 60px; text-align: left;
}
@media(max-width:640px){ .hero-cards { grid-template-columns: 1fr; } }
.glass-card {
  background: rgba(15,23,42,0.5);
  border: 1px solid var(--border-mid);
  border-radius: 24px;
  padding: 28px 32px;
  backdrop-filter: blur(16px);
}
.glass-card h3 {
  font-size: 16px; font-weight: 700; color: var(--text-primary);
  margin-bottom: 18px; display: flex; align-items: center; gap: 10px;
}
.card-icon { font-size: 20px; }
.glass-card ul { list-style: none; display: flex; flex-direction: column; gap: 12px; }
.glass-card ul li {
  display: flex; align-items: flex-start; gap: 12px;
  font-size: 14px; color: var(--text-secondary); line-height: 1.5;
}
.step-badge {
  flex-shrink: 0; width: 22px; height: 22px; border-radius: 50%;
  background: rgba(37,99,235,0.15); color: #3b82f6;
  display: flex; align-items: center; justify-content: center;
  font-size: 11px; font-weight: 700; margin-top: 1px;
}
.check-icon { color: #10b981; font-size: 13px; margin-top: 2px; flex-shrink: 0; }
.content-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px 24px; }
.content-item { display: flex; align-items: center; gap: 8px; font-size: 13px; color: var(--text-secondary); }

/* Stats bar */
.stats-bar {
  max-width: 900px; margin: 0 auto;
  display: flex; justify-content: center; gap: 60px;
  padding: 40px 24px;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}
@media(max-width:640px){ .stats-bar { gap: 30px; } }
.stat { text-align: center; }
.stat-num { font-size: 36px; font-weight: 800; letter-spacing: -1px; color: var(--text-primary); }
.stat-label { font-size: 12px; color: var(--text-muted); text-transform: uppercase; letter-spacing: 1px; margin-top: 2px; }

/* Features section */
.features {
  max-width: 1200px; margin: 0 auto;
  padding: 80px 24px;
}
.section-header { text-align: center; margin-bottom: 56px; }
.section-header h2 {
  font-size: clamp(28px, 4vw, 42px); font-weight: 800;
  letter-spacing: -1px;
  background: linear-gradient(135deg, #fff, rgba(248,250,252,0.5));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  margin-bottom: 12px;
}
.section-header p { font-size: 16px; color: var(--text-secondary); max-width: 520px; margin: 0 auto; font-weight: 300; }
.features-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 20px; }
.feature-card {
  background: rgba(15,23,42,0.4);
  border: 1px solid var(--border);
  border-radius: 20px; padding: 28px;
  backdrop-filter: blur(12px);
  transition: all 0.2s; cursor: default;
}
.feature-card:hover { border-color: rgba(37,99,235,0.4); transform: translateY(-2px); }
.feature-icon {
  width: 44px; height: 44px; border-radius: 14px;
  background: rgba(37,99,235,0.12);
  display: flex; align-items: center; justify-content: center;
  font-size: 20px; margin-bottom: 18px;
  transition: all 0.2s;
}
.feature-card:hover .feature-icon { background: #2563eb; transform: scale(1.1); }
.feature-card h3 { font-size: 16px; font-weight: 700; color: var(--text-primary); margin-bottom: 8px; }
.feature-card p { font-size: 13px; color: var(--text-secondary); line-height: 1.65; font-weight: 300; }

/* Chapters preview */
.chapters-section { padding: 60px 24px 80px; max-width: 1200px; margin: 0 auto; }
.chapters-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(200px,1fr)); gap: 12px; }
.chapter-pill {
  background: rgba(15,23,42,0.4); border: 1px solid var(--border);
  border-radius: 14px; padding: 14px 16px;
  display: flex; align-items: center; gap: 10px;
  transition: all 0.15s; cursor: pointer;
}
.chapter-pill:hover { border-color: rgba(37,99,235,0.4); background: rgba(37,99,235,0.06); }
.ch-num { font-size: 10px; font-weight: 700; color: #2563eb; min-width: 22px; }
.ch-name { font-size: 12px; color: var(--text-secondary); line-height: 1.3; }

/* Footer */
.footer {
  background: #020617;
  border-top: 1px solid var(--border);
  padding: 60px 24px 30px;
}
.footer-inner { max-width: 1200px; margin: 0 auto; }
.footer-top { display: grid; grid-template-columns: 2fr 1fr 1fr; gap: 40px; margin-bottom: 40px; }
@media(max-width:768px){ .footer-top { grid-template-columns: 1fr; } }
.footer-brand { display: flex; align-items: center; gap: 10px; margin-bottom: 14px; }
.footer-logo { width:30px;height:30px; background:linear-gradient(135deg,#2563eb,#4f46e5); border-radius:8px; display:flex;align-items:center;justify-content:center; font-weight:800;font-size:12px;color:#fff; }
.footer-brand-name { font-size:16px;font-weight:700;color:var(--text-primary); }
.footer-brand-name span { color:#3b82f6;opacity:0.5;font-weight:400; }
.footer-desc { font-size:13px;color:var(--text-muted);line-height:1.7;max-width:320px;margin-bottom:20px; }
.footer-links h4 { font-size:11px;font-weight:700;text-transform:uppercase;letter-spacing:1.5px;color:var(--text-secondary);margin-bottom:16px; }
.footer-links ul { list-style:none;display:flex;flex-direction:column;gap:10px; }
.footer-links a { font-size:13px;color:var(--text-muted);text-decoration:none;transition:color 0.15s; }
.footer-links a:hover { color:#38bdf8; }
.footer-bottom { border-top:1px solid var(--border); padding-top:24px;text-align:center; font-size:12px;color:var(--text-muted); }

/* ══════════════════════════════════════════════
   CLASSROOM / COURSE VIEW
══════════════════════════════════════════════ */

.classroom {
  display: flex; height: 100vh;
  overflow: hidden;
}

/* Sidebar */
.sidebar {
  width: 300px; min-width: 300px; height: 100vh;
  background: rgba(9,13,27,0.95);
  border-right: 1px solid var(--border);
  display: flex; flex-direction: column;
  backdrop-filter: blur(20px);
  overflow: hidden;
  position: relative; z-index: 10;
}

.sidebar-brand {
  padding: 18px 20px;
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center; gap: 12px;
}
.brand-logo {
  width: 40px; height: 40px;
  background: rgba(16,185,129,0.1);
  border: 1px solid rgba(16,185,129,0.2);
  border-radius: 12px;
  display: flex; align-items: center; justify-content: center;
  font-size: 22px;
}
.sidebar-brand h1 { font-size: 15px; font-weight: 700; color: var(--text-primary); letter-spacing: -0.2px; }
.sidebar-brand p { font-size: 10px; color: var(--text-muted); text-transform: uppercase; letter-spacing: 1px; margin-top: 1px; }

.overall-progress {
  padding: 14px 20px;
  border-bottom: 1px solid var(--border);
  background: rgba(30,41,59,0.2);
}
.progress-label {
  display: flex; justify-content: space-between; align-items: center;
  margin-bottom: 8px;
}
.progress-label span:first-child {
  font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: 1px;
  color: #10b981; background: rgba(16,185,129,0.1); padding: 2px 8px; border-radius: 99px;
}
.progress-label span:last-child {
  font-size: 20px; font-weight: 800; font-family: var(--font-mono); color: #10b981;
}
.progress-bar { height: 4px; background: rgba(255,255,255,0.05); border-radius: 99px; overflow: hidden; }
.progress-fill { height: 100%; background: #10b981; border-radius: 99px; transition: width 0.7s ease; }

#chapter-nav { flex: 1; overflow-y: auto; padding: 10px 0; }
#chapter-nav::-webkit-scrollbar { width: 3px; }
#chapter-nav::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.08); border-radius: 99px; }

.chapter-group { margin-bottom: 2px; }
.chapter-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 9px 20px;
  font-size: 12px; font-weight: 600; color: var(--text-muted);
  cursor: pointer; transition: all 0.15s;
  border-left: 2px solid transparent;
}
.chapter-header:hover { color: var(--text-secondary); background: rgba(255,255,255,0.03); }
.chapter-header.active-chapter { color: #3b82f6; border-left-color: #3b82f6; background: rgba(37,99,235,0.06); }
.ch-title { flex: 1; line-height: 1.3; padding-right: 6px; }
.ch-status { font-size: 10px; flex-shrink: 0; }

.lesson-list { display: none; padding-left: 8px; }
.lesson-list.open { display: block; }
.lesson-item {
  display: flex; align-items: center; gap: 8px;
  padding: 6px 20px 6px 24px;
  font-size: 12px; color: var(--text-muted);
  cursor: pointer; border-left: 2px solid transparent;
  transition: all 0.15s; line-height: 1.4;
}
.lesson-item:hover { color: var(--text-secondary); background: rgba(255,255,255,0.03); }
.lesson-item.active { color: #fff; border-left-color: #10b981; background: rgba(16,185,129,0.06); font-weight: 500; }
.lesson-item.completed { color: rgba(16,185,129,0.6); }
.li-icon { font-size: 9px; min-width: 12px; flex-shrink: 0; }

.sidebar-footer {
  padding: 14px 16px;
  border-top: 1px solid var(--border);
}
.back-btn {
  display: flex; align-items: center; gap: 8px;
  width: 100%; padding: 10px 14px;
  background: none; border: 1px solid var(--border);
  border-radius: 10px; color: var(--text-secondary);
  font-size: 13px; font-weight: 500; cursor: pointer;
  transition: all 0.15s; font-family: var(--font-sans);
}
.back-btn:hover { background: rgba(255,255,255,0.04); color: var(--text-primary); }

/* Main lesson area */
.lesson-main {
  flex: 1; height: 100vh;
  display: flex; flex-direction: column;
  overflow: hidden;
  background: var(--bg-base);
}

.lesson-header {
  padding: 22px 36px;
  border-bottom: 1px solid var(--border);
  background: rgba(9,13,27,0.6);
  backdrop-filter: blur(12px);
  display: flex; justify-content: space-between; align-items: center;
  flex-shrink: 0;
}
.lesson-header-left h2 { font-size: 20px; font-weight: 700; color: var(--text-primary); letter-spacing: -0.3px; }
.lesson-header-left p { font-size: 12px; color: var(--text-muted); margin-top: 3px; }
.complete-btn {
  display: flex; align-items: center; gap: 7px;
  padding: 9px 18px; border-radius: 10px;
  font-size: 13px; font-weight: 600; cursor: pointer;
  border: 1px solid rgba(16,185,129,0.3);
  background: rgba(16,185,129,0.08); color: #10b981;
  transition: all 0.15s; font-family: var(--font-sans);
}
.complete-btn:hover { background: rgba(16,185,129,0.16); }
.complete-btn.is-done { background: rgba(16,185,129,0.2); border-color: rgba(16,185,129,0.5); }

.lesson-scroll {
  flex: 1; overflow-y: auto;
  padding: 0;
  scroll-behavior: smooth;
  display: flex;
  gap: 0;
}
.lesson-scroll::-webkit-scrollbar { width: 5px; }
.lesson-scroll::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.08); border-radius: 99px; }

/* Main lesson body - takes available space */
.lesson-content-wrap {
  flex: 1;
  min-width: 0;
  padding: 44px 52px 80px;
  max-width: 820px;
}

/* Right info panel */
.lesson-info-panel {
  width: 280px;
  min-width: 280px;
  padding: 36px 24px;
  border-left: 1px solid var(--border);
  background: rgba(9,13,27,0.5);
  overflow-y: auto;
  position: sticky;
  top: 0;
  height: 100%;
}
.lesson-info-panel::-webkit-scrollbar { width: 3px; }
.lesson-info-panel::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.06); border-radius: 99px; }

.info-panel-section { margin-bottom: 32px; }

.info-panel-label {
  font-size: 9px;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 2px;
  color: var(--text-muted);
  margin-bottom: 14px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

.info-panel-objective {
  font-size: 13px;
  color: var(--text-secondary);
  line-height: 1.75;
  font-weight: 300;
}

.info-panel-skill {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 12px;
  margin-bottom: 6px;
  background: rgba(255,255,255,0.03);
  border: 1px solid var(--border);
  border-radius: 10px;
  font-size: 12px;
  color: var(--text-secondary);
  font-family: var(--font-mono);
  transition: all 0.15s;
}
.info-panel-skill:hover {
  border-color: rgba(16,185,129,0.3);
  color: #6ee7b7;
  background: rgba(16,185,129,0.04);
}
.skill-dot {
  width: 6px; height: 6px;
  border-radius: 50%;
  background: #10b981;
  flex-shrink: 0;
}

.info-panel-project {
  background: rgba(37,99,235,0.06);
  border: 1px solid rgba(37,99,235,0.2);
  border-radius: 12px;
  padding: 14px;
}
.info-panel-project-name {
  font-size: 13px;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 6px;
}
.info-panel-project-desc {
  font-size: 12px;
  color: var(--text-secondary);
  line-height: 1.6;
  font-weight: 300;
}

.info-chapter-progress {
  margin-top: 8px;
}
.icp-bar {
  height: 3px;
  background: rgba(255,255,255,0.05);
  border-radius: 99px;
  overflow: hidden;
  margin-top: 8px;
}
.icp-fill {
  height: 100%;
  background: linear-gradient(90deg, #2563eb, #10b981);
  border-radius: 99px;
  transition: width 0.5s ease;
}
.icp-label {
  display: flex;
  justify-content: space-between;
  font-size: 11px;
  color: var(--text-muted);
  margin-top: 5px;
  font-family: var(--font-mono);
}

.lesson-nav-bar {
  margin-top: 48px;
  padding-top: 28px; border-top: 1px solid var(--border);
  display: flex; justify-content: space-between; align-items: center;
}
.nav-btn {
  display: flex; align-items: center; gap: 7px;
  padding: 10px 20px; border-radius: 12px;
  font-size: 13px; font-weight: 600; cursor: pointer;
  border: 1px solid var(--border); background: transparent;
  color: var(--text-secondary); transition: all 0.15s;
  font-family: var(--font-sans);
}
.nav-btn:hover { color: var(--text-primary); border-color: rgba(255,255,255,0.15); background: rgba(255,255,255,0.04); }
.nav-btn:disabled { opacity: 0.3; cursor: default; }
.nav-btn.primary {
  background: #2563eb; color: #fff; border-color: #2563eb;
  box-shadow: 0 4px 14px rgba(37,99,235,0.3);
}
.nav-btn.primary:hover { background: #3b82f6; box-shadow: 0 6px 20px rgba(37,99,235,0.4); }

/* Mesh background glow for classroom */
.classroom-glow-1 {
  position: fixed; top: -20%; left: -20%; width: 50%; height: 50%;
  background: radial-gradient(circle, rgba(37,99,235,0.06) 0%, transparent 70%);
  pointer-events: none; z-index: 0;
}
.classroom-glow-2 {
  position: fixed; bottom: -20%; right: -20%; width: 50%; height: 50%;
  background: radial-gradient(circle, rgba(79,70,229,0.06) 0%, transparent 70%);
  pointer-events: none; z-index: 0;
}

/* ══════════════════════════════════════════════
   LESSON CONTENT COMPONENTS
══════════════════════════════════════════════ */

.lesson-tag {
  display: inline-block;
  font-size: 10px; font-weight: 700; text-transform: uppercase; letter-spacing: 1.5px;
  padding: 4px 14px; border-radius: 99px; margin-bottom: 16px;
  background: rgba(16,185,129,0.1); border: 1px solid rgba(16,185,129,0.2); color: #10b981;
}

.lesson-title {
  font-size: clamp(24px, 3.5vw, 34px); font-weight: 800;
  color: var(--text-primary); line-height: 1.15; letter-spacing: -0.8px; margin-bottom: 12px;
}

.lesson-meta {
  display: flex; gap: 20px; flex-wrap: wrap;
  margin-bottom: 32px; padding-bottom: 28px;
  border-bottom: 1px solid var(--border);
}
.lesson-meta span, .meta-item {
  font-size: 12px; color: var(--text-muted); display: flex; align-items: center; gap: 5px;
}

.lesson-section-title {
  font-size: 20px; font-weight: 700; color: var(--text-primary);
  margin: 36px 0 14px; letter-spacing: -0.3px;
}

.lesson-text {
  font-size: 15px; color: var(--text-secondary);
  line-height: 1.85; margin-bottom: 18px; font-weight: 300;
}

.lesson-text code, code {
  font-family: var(--font-mono); font-size: 12.5px;
  background: rgba(30,41,59,0.7); padding: 2px 7px;
  border-radius: 5px; color: #38bdf8;
  border: 1px solid rgba(255,255,255,0.08);
}

/* Code block */
.code-block {
  background: #050d1a; border: 1px solid rgba(255,255,255,0.08);
  border-radius: 16px; overflow: hidden; margin: 22px 0;
  box-shadow: 0 8px 32px rgba(0,0,0,0.4);
}
.code-block-header {
  display: flex; justify-content: space-between; align-items: center;
  padding: 10px 16px;
  background: rgba(255,255,255,0.03);
  border-bottom: 1px solid rgba(255,255,255,0.06);
}
.code-filename {
  font-family: var(--font-mono); font-size: 10px;
  color: var(--text-muted); text-transform: uppercase; letter-spacing: 1px;
}
.copy-btn {
  font-size: 10px; color: var(--text-muted); background: none; border: none;
  cursor: pointer; font-family: var(--font-sans);
  padding: 3px 8px; border-radius: 5px; transition: all 0.15s;
}
.copy-btn:hover { background: rgba(255,255,255,0.07); color: var(--text-primary); }
.code-block pre {
  padding: 20px; overflow-x: auto;
  font-family: var(--font-mono); font-size: 13px; line-height: 1.8;
  color: #e2e8f0;
}

/* Syntax */
.kw  { color: #f472b6; }
.fn  { color: #a78bfa; }
.st  { color: #7dd3fc; }
.cm  { color: #475569; font-style: italic; }
.nm  { color: #fbbf24; }
.op  { color: #64748b; }

/* Lab box */
.lab-box {
  margin: 24px 0; padding: 24px 28px;
  border: 1px solid rgba(6,182,212,0.2);
  border-left: 4px solid var(--accent-teal);
  background: rgba(6,182,212,0.04);
  border-radius: 18px;
}
.lab-box-title {
  font-size: 11px; font-weight: 800; text-transform: uppercase; letter-spacing: 1.5px;
  color: var(--accent-teal); margin-bottom: 16px; display: flex; align-items: center; gap: 8px;
}
.lab-box ol { padding-left: 18px; display: flex; flex-direction: column; gap: 10px; }
.lab-box ol li { font-size: 14px; color: var(--text-secondary); line-height: 1.6; }
.lab-box ol li::marker { color: var(--accent-teal); font-weight: 700; }

/* Lab steps (alt format) */
.lab-steps { display: flex; flex-direction: column; gap: 10px; }
.lab-step { display: flex; gap: 12px; align-items: flex-start; font-size: 13px; color: var(--text-secondary); line-height: 1.6; }
.step-num {
  min-width: 22px; height: 22px; border-radius: 50%;
  background: rgba(6,182,212,0.12); border: 1px solid rgba(6,182,212,0.25);
  color: var(--accent-teal); font-size: 11px; font-weight: 700;
  display: flex; align-items: center; justify-content: center;
  font-family: var(--font-mono); flex-shrink: 0; margin-top: 2px;
}

/* Tip / Warn */
.tip-box {
  margin: 18px 0; padding: 16px 20px;
  background: rgba(37,99,235,0.06); border: 1px solid rgba(37,99,235,0.2);
  border-left: 4px solid var(--accent-blue-lt);
  border-radius: 14px; font-size: 13.5px; color: #93c5fd; line-height: 1.7;
  display: flex; gap: 12px;
}
.warn-box {
  margin: 18px 0; padding: 16px 20px;
  background: rgba(245,158,11,0.06); border: 1px solid rgba(245,158,11,0.2);
  border-left: 4px solid var(--accent-amber);
  border-radius: 14px; font-size: 13.5px; color: #fcd34d; line-height: 1.7;
  display: flex; gap: 12px;
}

/* Stack diagram */
.stack-diagram { display: flex; flex-direction: column; gap: 4px; margin: 20px 0; }
.stack-layer { display: flex; align-items: center; gap: 14px; padding: 12px 18px; border-radius: 12px; border: 1px solid var(--border); font-size: 13px; }
.stack-layer.l1 { background: rgba(167,139,250,0.06); border-color: rgba(167,139,250,0.2); }
.stack-layer.l2 { background: rgba(96,165,250,0.06); border-color: rgba(96,165,250,0.2); }
.stack-layer.l3 { background: rgba(34,211,238,0.06); border-color: rgba(34,211,238,0.2); }
.stack-layer.l4 { background: rgba(52,211,153,0.06); border-color: rgba(52,211,153,0.2); }
.stack-num { font-family: var(--font-mono); font-size: 11px; font-weight: 700; min-width: 30px; height: 30px; border-radius: 8px; display: flex; align-items: center; justify-content: center; flex-shrink: 0; }
.l1 .stack-num { background: rgba(167,139,250,0.15); color: #c4b5fd; }
.l2 .stack-num { background: rgba(96,165,250,0.15); color: #93c5fd; }
.l3 .stack-num { background: rgba(34,211,238,0.15); color: #67e8f9; }
.l4 .stack-num { background: rgba(52,211,153,0.15); color: #6ee7b7; }
.stack-info { flex: 1; }
.stack-name { font-weight: 600; color: var(--text-primary); }
.stack-desc { font-size: 12px; color: var(--text-secondary); margin-top: 2px; }

/* Quiz */
.quiz-container { display: flex; flex-direction: column; gap: 20px; margin: 20px 0; }
.quiz-question {
  background: rgba(15,23,42,0.5); border: 1px solid var(--border);
  border-radius: 18px; padding: 22px;
  backdrop-filter: blur(8px);
}
.quiz-q-text { font-size: 15px; font-weight: 600; color: var(--text-primary); margin-bottom: 14px; line-height: 1.5; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-option {
  display: flex; align-items: flex-start; gap: 12px;
  padding: 12px 16px;
  background: rgba(2,6,23,0.5);
  border: 1px solid var(--border);
  border-radius: 12px; cursor: pointer;
  font-size: 13.5px; color: var(--text-secondary);
  text-align: left; width: 100%;
  font-family: var(--font-sans); line-height: 1.5;
  transition: all 0.15s;
}
.quiz-option:hover:not(:disabled) { border-color: rgba(96,165,250,0.4); background: rgba(37,99,235,0.06); color: var(--text-primary); }
.quiz-option.correct { border-color: rgba(16,185,129,0.5); background: rgba(16,185,129,0.1); color: #6ee7b7; }
.quiz-option.wrong { border-color: rgba(239,68,68,0.5); background: rgba(239,68,68,0.08); color: #fca5a5; }
.quiz-option:disabled { cursor: default; }
.opt-letter { font-weight: 700; color: var(--text-muted); min-width: 18px; flex-shrink: 0; }
.quiz-option.correct .opt-letter { color: #6ee7b7; }
.quiz-option.wrong .opt-letter { color: #fca5a5; }
.quiz-explanation { margin-top: 12px; padding: 12px 16px; background: rgba(255,255,255,0.03); border-left: 3px solid var(--accent-teal); border-radius: 8px; font-size: 13px; color: var(--text-muted); line-height: 1.6; }

/* Legacy quiz style (quiz-opt) */
.quiz-opt { display:flex;align-items:center;gap:8px;padding:10px 14px;border-radius:10px;border:1px solid var(--border);font-size:13px;color:var(--text-secondary);cursor:pointer;transition:all .15s;background:rgba(2,6,23,.5);width:100%;font-family:var(--font-sans); }
.quiz-opt:hover{border-color:rgba(96,165,250,.4);color:var(--text-primary);}
.quiz-opt.correct{border-color:rgba(16,185,129,.5);background:rgba(16,185,129,.1);color:#6ee7b7;}
.quiz-opt.wrong{border-color:rgba(239,68,68,.5);background:rgba(239,68,68,.08);color:#fca5a5;}
.quiz-dot{width:14px;height:14px;border-radius:50%;border:1.5px solid var(--border);flex-shrink:0;transition:all .15s;}
.quiz-opt.correct .quiz-dot{border-color:#10b981;background:#10b981;}
.quiz-opt.wrong .quiz-dot{border-color:#ef4444;background:#ef4444;}
.quiz-feedback{margin-top:8px;font-size:12px;padding:7px 12px;border-radius:8px;}
.correct-fb{background:rgba(16,185,129,.1);color:#6ee7b7;}
.wrong-fb{background:rgba(239,68,68,.08);color:#fca5a5;}

.quiz-score-bar { text-align: right; font-size: 12px; color: var(--accent-teal); margin-top: 8px; font-family: var(--font-mono); }

/* Lists */
ul, ol { color: var(--text-secondary); font-size: 14px; line-height: 1.9; padding-left: 22px; margin-bottom: 16px; }
li { margin-bottom: 5px; }
strong { color: var(--text-primary); font-weight: 600; }
em { font-style: italic; }

@media(max-width:768px){
  .sidebar { display: none; }
  .lesson-scroll { padding: 24px 20px 48px; }
}