/* ============================================================
   style.css — codewithcopilot.ai
   Clean, modern developer-education design
   ============================================================ */

/* ── Variables ─────────────────────────────────────────── */
:root {
  --primary:        #1d4ed8;
  --primary-light:  #3b82f6;
  --primary-dark:   #1e3a8a;
  --accent:         #06b6d4;

  --sidebar-bg:     #0f172a;
  --sidebar-text:   #cbd5e1;
  --sidebar-hover:  #1e293b;
  --sidebar-active: #1e3a5f;
  --sidebar-border: #1e293b;
  --sidebar-done:   #166534;

  --bg:             #f1f5f9;
  --card-bg:        #ffffff;
  --text:           #0f172a;
  --text-muted:     #64748b;
  --border:         #e2e8f0;

  --success:        #16a34a;
  --success-bg:     #f0fdf4;
  --warning:        #d97706;
  --warning-bg:     #fffbeb;
  --danger:         #dc2626;
  --danger-bg:      #fef2f2;

  --hero-bg:        #0f172a;
  --hero-text:      #f8fafc;

  --radius:         8px;
  --radius-lg:      12px;
  --shadow:         0 1px 3px rgba(0,0,0,.08), 0 1px 2px rgba(0,0,0,.06);
  --shadow-md:      0 4px 6px rgba(0,0,0,.07), 0 2px 4px rgba(0,0,0,.06);
  --shadow-lg:      0 10px 15px rgba(0,0,0,.08), 0 4px 6px rgba(0,0,0,.05);

  --font:           'Inter', system-ui, -apple-system, sans-serif;
  --mono:           'JetBrains Mono', 'Fira Code', 'Consolas', monospace;

  --sidebar-w:      280px;
  --header-h:       60px;
}

/* ── Reset ──────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
}
a { color: var(--primary); text-decoration: none; }
a:hover { color: var(--primary-dark); text-decoration: underline; }
img, svg { display: block; max-width: 100%; }
button { cursor: pointer; font-family: inherit; }

/* ── Scrollbar ───────────────────────────────────────────  */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

/* ── Typography ─────────────────────────────────────────── */
h1 { font-size: 2.25rem; font-weight: 800; line-height: 1.2; }
h2 { font-size: 1.5rem;  font-weight: 700; line-height: 1.3; }
h3 { font-size: 1.125rem; font-weight: 600; }
h4 { font-size: 1rem; font-weight: 600; }
p  { color: var(--text-muted); }

/* ── Global Header ──────────────────────────────────────── */
.site-header {
  height: var(--header-h);
  background: var(--hero-bg);
  border-bottom: 1px solid #1e293b;
  display: flex;
  align-items: center;
  padding: 0 24px;
  position: sticky;
  top: 0;
  z-index: 100;
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
}
.site-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 1.05rem;
  color: #f8fafc;
  text-decoration: none;
}
.site-logo:hover { color: var(--accent); text-decoration: none; }
.logo-icon {
  width: 32px; height: 32px;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  border-radius: 8px;
  display: flex; align-items: center; justify-content: center;
  font-size: 16px;
  flex-shrink: 0;
}
.site-nav {
  display: flex;
  align-items: center;
  gap: 6px;
}
.site-nav a {
  color: #94a3b8;
  font-size: 0.9rem;
  padding: 6px 12px;
  border-radius: var(--radius);
  transition: background .15s, color .15s;
  text-decoration: none;
}
.site-nav a:hover { background: #1e293b; color: #f8fafc; text-decoration: none; }
.site-nav a.active { background: var(--primary); color: #fff; }

/* ── Footer ─────────────────────────────────────────────── */
.site-footer {
  background: var(--hero-bg);
  color: #64748b;
  text-align: center;
  padding: 32px 24px;
  font-size: 0.85rem;
  margin-top: 80px;
}
.site-footer a { color: #94a3b8; }
.site-footer a:hover { color: #f8fafc; }

/* ── Buttons ─────────────────────────────────────────────── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  border-radius: var(--radius);
  font-size: 0.9rem;
  font-weight: 600;
  border: none;
  transition: all .15s;
  white-space: nowrap;
}
.btn-primary {
  background: var(--primary);
  color: #fff;
}
.btn-primary:hover { background: var(--primary-dark); transform: translateY(-1px); box-shadow: var(--shadow-md); color: #fff; text-decoration: none; }
.btn-outline {
  background: transparent;
  color: var(--primary);
  border: 2px solid var(--primary);
}
.btn-outline:hover { background: var(--primary); color: #fff; text-decoration: none; }
.btn-ghost {
  background: transparent;
  color: var(--text-muted);
  border: 1px solid var(--border);
}
.btn-ghost:hover { background: var(--bg); color: var(--text); text-decoration: none; }
.btn-lg { padding: 14px 28px; font-size: 1rem; border-radius: var(--radius-lg); }
.btn-sm { padding: 6px 14px; font-size: 0.8rem; }

/* ── Badges ──────────────────────────────────────────────── */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 3px 10px;
  border-radius: 100px;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: .02em;
}
.badge-blue  { background: #dbeafe; color: var(--primary-dark); }
.badge-green { background: #dcfce7; color: #166534; }
.badge-gray  { background: #f1f5f9; color: #64748b; }
.badge-amber { background: #fef3c7; color: #92400e; }
.badge-level {
  background: linear-gradient(135deg, var(--primary), var(--accent));
  color: #fff;
  font-size: 0.7rem;
  padding: 2px 8px;
}

/* ── Series tag ──────────────────────────────────────────── */
.series-tag {
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: .06em;
  text-transform: uppercase;
  color: var(--text-muted);
}

/* ═══════════════════════════════════════════════════════════
   LANDING PAGE (index.html)
═══════════════════════════════════════════════════════════ */

/* Hero */
.hero {
  background: var(--hero-bg);
  background-image:
    radial-gradient(circle at 20% 50%, rgba(29,78,216,.25) 0%, transparent 50%),
    radial-gradient(circle at 80% 20%, rgba(6,182,212,.15) 0%, transparent 40%);
  color: var(--hero-text);
  padding: 96px 24px 80px;
  text-align: center;
}
.hero-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: rgba(29,78,216,.25);
  border: 1px solid rgba(59,130,246,.3);
  color: #93c5fd;
  padding: 6px 14px;
  border-radius: 100px;
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: .05em;
  margin-bottom: 24px;
}
.hero h1 {
  font-size: clamp(2rem, 5vw, 3.25rem);
  color: #f8fafc;
  max-width: 700px;
  margin: 0 auto 20px;
}
.hero h1 span {
  background: linear-gradient(90deg, var(--primary-light), var(--accent));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-sub {
  font-size: 1.1rem;
  color: #94a3b8;
  max-width: 540px;
  margin: 0 auto 36px;
  line-height: 1.7;
}
.hero-cta {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
}
.hero-stats {
  display: flex;
  gap: 32px;
  justify-content: center;
  flex-wrap: wrap;
  margin-top: 56px;
  padding-top: 40px;
  border-top: 1px solid #1e293b;
}
.hero-stat { text-align: center; }
.hero-stat-value {
  font-size: 1.75rem;
  font-weight: 800;
  color: #f8fafc;
  display: block;
}
.hero-stat-label {
  font-size: 0.8rem;
  color: #64748b;
  letter-spacing: .04em;
}

/* Levels Section */
.section {
  max-width: 1100px;
  margin: 0 auto;
  padding: 72px 24px;
}
.section-header {
  text-align: center;
  margin-bottom: 48px;
}
.section-header h2 { margin-bottom: 10px; }
.section-header p  { max-width: 500px; margin: 0 auto; }
.section-label {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--primary);
  margin-bottom: 8px;
}

/* Level Cards */
.level-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 20px;
}
.level-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px;
  box-shadow: var(--shadow);
  transition: transform .15s, box-shadow .15s;
}
.level-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}
.level-card-icon {
  width: 48px; height: 48px;
  border-radius: var(--radius);
  display: flex; align-items: center; justify-content: center;
  font-size: 22px;
  margin-bottom: 16px;
}
.level-card h3 { margin-bottom: 8px; }
.level-card p  { font-size: 0.875rem; }
.level-card-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: 16px;
}

/* What you'll learn */
.tools-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 16px;
}
.tool-chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 12px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 100px;
  font-size: 0.8rem;
  font-weight: 500;
}

/* CTA Banner */
.cta-banner {
  background: linear-gradient(135deg, var(--primary-dark), var(--primary));
  border-radius: var(--radius-lg);
  padding: 56px 40px;
  text-align: center;
  color: #fff;
  margin: 0 24px;
  max-width: 1100px;
  margin: 0 auto 80px;
}
.cta-banner h2 { color: #fff; margin-bottom: 12px; }
.cta-banner p  { color: rgba(255,255,255,.75); margin-bottom: 28px; }

/* ═══════════════════════════════════════════════════════════
   LEARN PAGE (learn.html)
═══════════════════════════════════════════════════════════ */

.learn-page { max-width: 1100px; margin: 0 auto; padding: 48px 24px; }

/* Progress Banner */
.progress-banner {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px 32px;
  margin-bottom: 40px;
  display: flex;
  align-items: center;
  gap: 32px;
  box-shadow: var(--shadow);
}
.progress-text { flex: 1; }
.progress-text h2 { font-size: 1.125rem; margin-bottom: 4px; }
.progress-text p  { font-size: 0.85rem; }
.progress-bar-wrap {
  flex: 2;
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.progress-bar-bg {
  background: var(--border);
  border-radius: 100px;
  height: 10px;
  overflow: hidden;
}
.progress-bar-fill {
  background: linear-gradient(90deg, var(--primary), var(--accent));
  height: 100%;
  border-radius: 100px;
  transition: width .5s ease;
}
.progress-bar-label {
  font-size: 0.78rem;
  color: var(--text-muted);
  text-align: right;
}

/* Series Section */
.series-section { margin-bottom: 48px; }
.series-title {
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--text-muted);
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 16px;
}
.modules-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 16px;
}

/* Module Card */
.module-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  box-shadow: var(--shadow);
  transition: transform .15s, box-shadow .15s;
  cursor: pointer;
  text-decoration: none;
  color: inherit;
}
.module-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: #bfdbfe;
  text-decoration: none;
  color: inherit;
}
.module-card.completed { border-color: #bbf7d0; background: #f0fdf4; }
.module-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 8px;
}
.module-card h3 {
  font-size: 0.925rem;
  font-weight: 600;
  line-height: 1.4;
  color: var(--text);
}
.module-status-icon {
  width: 22px; height: 22px;
  border-radius: 50%;
  flex-shrink: 0;
  display: flex; align-items: center; justify-content: center;
  font-size: 11px;
}
.status-done  { background: var(--success-bg); color: var(--success); }
.status-todo  { background: var(--border); color: var(--text-muted); }
.module-card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.module-duration {
  font-size: 0.78rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 4px;
}
.quiz-score {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--success);
}

/* ═══════════════════════════════════════════════════════════
   LESSON PAGE (lesson.html)
═══════════════════════════════════════════════════════════ */

.lesson-layout {
  display: flex;
  height: calc(100vh - var(--header-h));
  overflow: hidden;
}

/* ── Sidebar ─────────────────────────────────────────────── */
.lesson-sidebar {
  width: var(--sidebar-w);
  background: var(--sidebar-bg);
  border-right: 1px solid var(--sidebar-border);
  display: flex;
  flex-direction: column;
  overflow: hidden;
  flex-shrink: 0;
}
.sidebar-header {
  padding: 16px 20px;
  border-bottom: 1px solid var(--sidebar-border);
}
.sidebar-header-title {
  font-size: 0.8rem;
  font-weight: 700;
  color: #f8fafc;
  margin-bottom: 4px;
}
.sidebar-progress-text {
  font-size: 0.72rem;
  color: #64748b;
}
.sidebar-progress-bar {
  margin-top: 10px;
  height: 3px;
  background: #1e293b;
  border-radius: 100px;
  overflow: hidden;
}
.sidebar-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: 100px;
  transition: width .5s ease;
}
.sidebar-nav {
  flex: 1;
  overflow-y: auto;
  padding: 8px 0;
}
.sidebar-series-label {
  font-size: 0.65rem;
  font-weight: 700;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: #475569;
  padding: 16px 20px 4px;
}
.sidebar-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 20px;
  cursor: pointer;
  transition: background .1s;
  border: none;
  background: none;
  width: 100%;
  text-align: left;
  text-decoration: none;
}
.sidebar-item:hover  { background: var(--sidebar-hover); }
.sidebar-item.active { background: var(--sidebar-active); }
.sidebar-item-indicator {
  width: 18px; height: 18px;
  border-radius: 50%;
  border: 2px solid #334155;
  display: flex; align-items: center; justify-content: center;
  font-size: 9px;
  flex-shrink: 0;
  transition: all .15s;
}
.sidebar-item.done .sidebar-item-indicator {
  background: var(--success);
  border-color: var(--success);
  color: #fff;
}
.sidebar-item.active .sidebar-item-indicator {
  border-color: var(--primary-light);
  background: rgba(59,130,246,.15);
}
.sidebar-item-text {
  flex: 1;
  min-width: 0;
}
.sidebar-item-level {
  font-size: 0.65rem;
  font-weight: 700;
  color: #475569;
  letter-spacing: .04em;
}
.sidebar-item-title {
  font-size: 0.78rem;
  color: var(--sidebar-text);
  line-height: 1.35;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.sidebar-item.active .sidebar-item-title { color: #fff; }

/* ── Lesson Main ─────────────────────────────────────────── */
.lesson-main {
  flex: 1;
  overflow-y: auto;
  background: var(--bg);
}
.lesson-content {
  max-width: 860px;
  margin: 0 auto;
  padding: 40px 32px 80px;
}

/* Breadcrumb */
.breadcrumb {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-bottom: 24px;
}
.breadcrumb a { color: var(--text-muted); }
.breadcrumb a:hover { color: var(--primary); }
.breadcrumb-sep { color: var(--border); }

/* Lesson header */
.lesson-header { margin-bottom: 28px; }
.lesson-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 12px;
  flex-wrap: wrap;
}
.lesson-header h1 {
  font-size: 1.75rem;
  color: var(--text);
  margin-bottom: 8px;
}
.lesson-duration {
  font-size: 0.85rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 4px;
}

/* Video embed */
.video-wrapper {
  position: relative;
  padding-bottom: 56.25%; /* 16:9 */
  height: 0;
  overflow: hidden;
  border-radius: var(--radius-lg);
  background: #000;
  margin-bottom: 32px;
  box-shadow: var(--shadow-lg);
}
.video-wrapper iframe {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  border: none;
  border-radius: var(--radius-lg);
}
.video-placeholder {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 12px;
  background: #1e293b;
  color: #94a3b8;
  border-radius: var(--radius-lg);
  font-size: 0.9rem;
  text-align: center;
  padding: 24px;
}
.video-placeholder-icon { font-size: 3rem; opacity: .4; }

/* Content blocks */
.content-block {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px 28px;
  margin-bottom: 20px;
  box-shadow: var(--shadow);
}
.content-block h3 {
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--text-muted);
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.content-block ul {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.content-block ul li {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  font-size: 0.9rem;
  color: var(--text);
  line-height: 1.55;
}
.content-block ul li::before {
  content: '';
  width: 6px; height: 6px;
  border-radius: 50%;
  background: var(--primary-light);
  margin-top: 8px;
  flex-shrink: 0;
}
.content-block.takeaways { border-left: 4px solid var(--accent); }
.content-block.resources ul li::before { display: none; }
.content-block.resources ul li a {
  color: var(--primary);
  font-size: 0.9rem;
  display: flex;
  align-items: center;
  gap: 6px;
}
.content-block.resources ul li a:hover { text-decoration: underline; }

/* Take Quiz button */
.take-quiz-btn-wrap {
  text-align: center;
  margin: 36px 0 24px;
}
.take-quiz-btn-wrap p {
  font-size: 0.85rem;
  margin-bottom: 16px;
}

/* ── Quiz Section ─────────────────────────────────────────── */
.quiz-section {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow);
  margin-top: 32px;
}
.quiz-header {
  background: var(--hero-bg);
  color: #f8fafc;
  padding: 20px 28px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.quiz-header h2 { font-size: 1rem; color: #f8fafc; }
.quiz-score-display {
  font-size: 0.85rem;
  color: #94a3b8;
  display: flex;
  align-items: center;
  gap: 6px;
}
.quiz-score-display strong { color: #4ade80; }
.quiz-body { padding: 28px; }
.question-block {
  margin-bottom: 28px;
  padding-bottom: 28px;
  border-bottom: 1px solid var(--border);
}
.question-block:last-of-type { border-bottom: none; }
.question-number {
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: .06em;
  text-transform: uppercase;
  color: var(--primary);
  margin-bottom: 6px;
}
.question-text {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text);
  line-height: 1.45;
  margin-bottom: 14px;
}
.question-type-hint {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-bottom: 12px;
  font-style: italic;
}
.options-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.option-label {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 10px 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  cursor: pointer;
  transition: all .1s;
  font-size: 0.875rem;
  color: var(--text);
  line-height: 1.45;
}
.option-label:hover { border-color: var(--primary-light); background: #eff6ff; }
.option-label input { margin-top: 2px; accent-color: var(--primary); flex-shrink: 0; }
.option-label.correct   { border-color: var(--success); background: var(--success-bg); }
.option-label.incorrect { border-color: var(--danger);  background: var(--danger-bg);  }
.option-label.missed    { border-color: var(--success); background: var(--success-bg); opacity: .7; }

/* Quiz footer */
.quiz-footer {
  padding: 20px 28px;
  border-top: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
}
.quiz-result-msg {
  font-size: 0.9rem;
  font-weight: 600;
}
.quiz-result-msg.pass { color: var(--success); }
.quiz-result-msg.fail { color: var(--warning); }

/* Next / Prev navigation */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  gap: 12px;
}
.lesson-nav-link {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 18px;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  background: var(--card-bg);
  transition: all .15s;
  max-width: 220px;
}
.lesson-nav-link:hover { border-color: var(--primary-light); box-shadow: var(--shadow-md); text-decoration: none; }
.lesson-nav-link.next { text-align: right; }
.lesson-nav-label { font-size: 0.7rem; text-transform: uppercase; letter-spacing: .06em; color: var(--text-muted); }
.lesson-nav-title { font-size: 0.85rem; font-weight: 600; color: var(--text); }
.lesson-nav-empty { flex: 1; }

/* ═══════════════════════════════════════════════════════════
   RESPONSIVE
═══════════════════════════════════════════════════════════ */
@media (max-width: 768px) {
  :root { --sidebar-w: 0px; }
  .lesson-sidebar { display: none; }
  .lesson-content { padding: 24px 16px 60px; }
  .lesson-layout  { overflow-y: auto; }
  .lesson-main    { overflow-y: visible; }
  h1 { font-size: 1.75rem; }
  .progress-banner { flex-direction: column; align-items: flex-start; }
  .modules-grid { grid-template-columns: 1fr; }
  .hero { padding: 60px 16px 48px; }
  .hero-stats { gap: 20px; }
  .site-nav a span { display: none; }
}
@media (max-width: 480px) {
  .lesson-header h1 { font-size: 1.35rem; }
  .hero h1 { font-size: 1.75rem; }
  .quiz-footer { flex-direction: column-reverse; align-items: stretch; }
  .quiz-footer .btn { text-align: center; justify-content: center; }
}

/* ── Utility ─────────────────────────────────────────────── */
.text-center { text-align: center; }
.text-muted  { color: var(--text-muted); }
.mt-4  { margin-top: 16px; }
.mt-8  { margin-top: 32px; }
.mb-4  { margin-bottom: 16px; }
.hidden { display: none !important; }
.flex   { display: flex; }
.items-center { align-items: center; }
.gap-2  { gap: 8px; }
.gap-4  { gap: 16px; }