/* ═══════════════════════════════════════════════════════════════
   FEYNOTES — Design System
   All colors managed by base.css via CSS custom properties.
   This file handles layout, typography, and components only.
   ═══════════════════════════════════════════════════════════════ */

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

/* ─── LAYOUT TOKENS (non-color) ─── */
:root {
  --sidebar-w: 260px;
  --header-h: 52px;
  --radius: 10px;
  --radius-sm: 6px;
  --radius-lg: 14px;
  --font-body: 'Outfit', system-ui, -apple-system, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  --transition: 0.2s ease;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { font-size: 16px; scroll-behavior: smooth; }

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.72;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

::selection { background: var(--accent); color: #fff; }
::-webkit-scrollbar { width: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-light); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

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

/* ═══════════════════════════════════════════════════════════════
   HEADER
   ═══════════════════════════════════════════════════════════════ */
#site-header {
  position: fixed; top: 0; left: 0; right: 0;
  height: var(--header-h);
  background: var(--header-bg);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center;
  padding: 0 24px;
  z-index: 200;
  gap: 16px;
}

.header-home {
  font-family: var(--font-mono);
  font-size: 0.85rem; font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  display: flex; align-items: center; gap: 0;
  transition: color var(--transition);
}
.header-home:hover { color: var(--text-primary); }
.header-home-accent { color: var(--accent); }
.header-cursor {
  display: inline-block; width: 1.5px; height: 14px;
  background: var(--accent); margin-left: 2px;
  vertical-align: middle;
  animation: headerBlink 1s step-end infinite;
}
@keyframes headerBlink { 0%, 100% { opacity: 1; } 50% { opacity: 0; } }
.header-sep {
  color: var(--border-light); font-size: 1rem; font-weight: 300;
  margin: 0 10px; user-select: none;
}
.header-logo {
  font-size: 1.05rem; font-weight: 700;
  color: var(--accent); white-space: nowrap;
  letter-spacing: -0.3px; user-select: none;
  display: flex; align-items: center; gap: 8px;
}
.header-logo .logo-icon { font-size: 1.2rem; }
.header-logo .logo-sub {
  color: var(--text-muted); font-weight: 400;
  font-size: 0.78rem; margin-left: 4px;
}
.header-nav { display: flex; gap: 2px; margin-left: auto; }
.header-nav a {
  font-size: 0.82rem; color: var(--text-muted);
  padding: 6px 14px; border-radius: var(--radius-sm);
  transition: all var(--transition); font-weight: 500;
}
.header-nav a:hover { color: var(--text-secondary); background: var(--bg-hover); }
.header-nav a.active { color: var(--accent); background: var(--accent-glow); }

/* ═══════════════════════════════════════════════════════════════
   INDEX PAGE
   ═══════════════════════════════════════════════════════════════ */
.page-wrapper {
  margin-top: var(--header-h);
  min-height: calc(100vh - var(--header-h));
  padding: 48px 32px 80px;
  max-width: 1100px; margin-left: auto; margin-right: auto;
}
.hero { text-align: center; margin-bottom: 56px; padding: 48px 0 32px; }
.hero h1 {
  font-size: 2.8rem; font-weight: 800; letter-spacing: -1px;
  background: linear-gradient(135deg, var(--text-primary) 0%, var(--accent) 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text; margin-bottom: 12px;
}
.hero p { font-size: 1.05rem; color: var(--text-muted); max-width: 550px; margin: 0 auto; font-weight: 300; }
.hero .hero-badge {
  display: inline-block; background: var(--accent-glow); color: var(--accent);
  font-size: 0.75rem; font-weight: 600; padding: 4px 12px; border-radius: 20px;
  margin-bottom: 16px; letter-spacing: 0.5px; text-transform: uppercase;
}
.lessons-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 16px; }
.lesson-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius-lg); padding: 24px;
  transition: all 0.3s ease; cursor: pointer; text-decoration: none;
  display: block; position: relative; overflow: hidden;
}
.lesson-card::before {
  content: ''; position: absolute; top: 0; left: 0; right: 0; height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--purple));
  opacity: 0; transition: opacity 0.3s ease;
}
.lesson-card:hover {
  border-color: var(--border-light); background: var(--bg-hover);
  transform: translateY(-2px); box-shadow: 0 8px 32px rgba(0,0,0,0.15);
}
.lesson-card:hover::before { opacity: 1; }
.lesson-card .card-num { font-size: 0.7rem; font-weight: 700; color: var(--accent); letter-spacing: 1.5px; text-transform: uppercase; margin-bottom: 8px; }
.lesson-card .card-title { font-size: 1.05rem; font-weight: 600; color: var(--text-primary); margin-bottom: 8px; line-height: 1.4; }
.lesson-card .card-abstract { font-size: 0.82rem; color: var(--text-muted); line-height: 1.5; font-weight: 300; }
.lesson-card .card-date { font-size: 0.72rem; color: var(--text-muted); margin-top: 14px; font-family: var(--font-mono); }
.section-header { margin: 48px 0 20px; display: flex; align-items: center; gap: 12px; }
.section-header h2 { font-size: 1.3rem; font-weight: 700; color: var(--text-primary); }
.section-header .section-line { flex: 1; height: 1px; background: var(--border); }

/* ═══════════════════════════════════════════════════════════════
   LESSON PAGE
   ═══════════════════════════════════════════════════════════════ */
.lesson-layout { margin-top: var(--header-h); display: flex; min-height: calc(100vh - var(--header-h)); }
.lesson-sidebar {
  width: var(--sidebar-w); min-width: var(--sidebar-w);
  position: sticky; top: var(--header-h); height: calc(100vh - var(--header-h));
  align-self: flex-start; background: var(--bg-secondary);
  border-right: 1px solid var(--border); overflow-y: auto; padding: 20px 0;
  transition: width 0.3s ease, min-width 0.3s ease, padding 0.3s ease;
}
.lesson-sidebar.closed { width: 0; min-width: 0; overflow: hidden; padding: 0; }
.sidebar-toggle {
  position: fixed; top: calc(var(--header-h) + 12px); left: calc(var(--sidebar-w) + 12px);
  z-index: 150; width: 36px; height: 36px; border-radius: var(--radius-sm);
  background: var(--bg-card); border: 1px solid var(--border); color: var(--text-muted);
  font-size: 1.1rem; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: left 0.3s ease, background var(--transition), color var(--transition);
}
.sidebar-toggle:hover { background: var(--bg-hover); color: var(--accent); border-color: var(--accent-dim); }
.sidebar-toggle.collapsed { left: 12px; }
.sidebar-title { font-size: 0.68rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.5px; color: var(--text-muted); padding: 0 20px; margin-bottom: 12px; }
.sidebar-link {
  display: flex; align-items: flex-start; gap: 10px; padding: 7px 20px;
  font-size: 0.82rem; color: var(--text-secondary); text-decoration: none; cursor: pointer;
  transition: all var(--transition); border-left: 2px solid transparent; line-height: 1.4;
}
.sidebar-link:hover { color: var(--text-primary); background: var(--bg-hover); }
.sidebar-link.active { color: var(--accent); border-left-color: var(--accent); background: var(--accent-glow); }
.sidebar-link .sl-icon { font-size: 0.85rem; flex-shrink: 0; margin-top: 1px; }
.sidebar-back { display: flex; align-items: center; gap: 8px; padding: 10px 20px; margin-bottom: 16px; font-size: 0.82rem; color: var(--text-muted); text-decoration: none; transition: all var(--transition); }
.sidebar-back:hover { color: var(--accent); }
.sidebar-nav-buttons { padding: 16px 20px 0; margin-top: 16px; border-top: 1px solid var(--border); display: flex; gap: 8px; }
.sidebar-nav-buttons a { flex: 1; text-align: center; padding: 8px; border-radius: var(--radius-sm); font-size: 0.78rem; font-weight: 500; background: var(--bg-tertiary); color: var(--text-muted); transition: all var(--transition); }
.sidebar-nav-buttons a:hover { background: var(--bg-hover); color: var(--text-primary); }
.lesson-content { flex: 1; overflow-y: visible; padding: 36px 80px 80px; }
.lesson-content > * { max-width: 1000px; margin-left: auto; margin-right: auto; }

.lesson-header { margin-bottom: 40px; }
.lesson-header .lesson-num { font-size: 0.72rem; font-weight: 700; color: var(--accent); letter-spacing: 1.5px; text-transform: uppercase; margin-bottom: 8px; }
.lesson-header h1 {
  font-size: 2rem; font-weight: 800; letter-spacing: -0.5px;
  background: linear-gradient(135deg, var(--text-primary), var(--accent));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text; margin-bottom: 10px;
}
.lesson-abstract { font-size: 0.92rem; color: var(--text-muted); font-style: italic; border-left: 3px solid var(--border-light); padding-left: 16px; max-width: 650px; font-weight: 300; }

.content-section { margin-bottom: 40px; scroll-margin-top: calc(var(--header-h) + 24px); }
.content-section h2 { font-size: 1.3rem; font-weight: 700; margin-bottom: 16px; display: flex; align-items: center; gap: 10px; color: var(--text-primary); }
.content-section h2 .sec-icon { font-size: 1.15rem; }
.content-section h3 { font-size: 1.05rem; font-weight: 600; margin: 20px 0 10px; color: var(--text-primary); }
.content-section p { margin-bottom: 12px; color: var(--text-secondary); font-weight: 400; }
.content-section p strong { color: var(--text-primary); font-weight: 600; }

/* ─── Component Boxes ─── */
.formula-box { background: var(--gold-dim); border: 1px solid rgba(240,192,80,0.2); border-radius: var(--radius); padding: 20px 24px; margin: 16px 0; }
.formula-box .fb-title { font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.2px; color: var(--gold); margin-bottom: 14px; }
.formula-item { display: flex; align-items: baseline; gap: 12px; margin-bottom: 10px; }
.formula-item:last-child { margin-bottom: 0; }
.formula-label { font-size: 0.78rem; color: var(--text-muted); white-space: nowrap; min-width: 130px; }
.formula-katex { font-size: 1.05rem; }

.steps-box { background: var(--blue-dim); border: 1px solid rgba(116,192,252,0.18); border-radius: var(--radius); padding: 20px 24px; margin: 16px 0; }
.steps-box .sb-title { font-size: 0.7rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1.2px; color: var(--blue); margin-bottom: 14px; }
.step-item { display: flex; align-items: flex-start; gap: 14px; margin-bottom: 12px; }
.step-item:last-child { margin-bottom: 0; }
.step-num { width: 24px; height: 24px; border-radius: 50%; background: rgba(116,192,252,0.15); color: var(--blue); font-weight: 700; font-size: 0.75rem; display: flex; align-items: center; justify-content: center; flex-shrink: 0; margin-top: 2px; }
.step-text { color: var(--text-secondary); font-size: 0.9rem; line-height: 1.6; }
.step-text strong { color: var(--text-primary); }

.alert-box { background: var(--red-dim); border: 1px solid rgba(255,107,107,0.2); border-radius: var(--radius); padding: 20px 24px; margin: 16px 0; }
.alert-box .ab-title { font-size: 0.9rem; font-weight: 700; color: var(--red); margin-bottom: 10px; }
.alert-box p { color: var(--text-secondary); }

.quote-box { background: var(--purple-dim); border: 1px solid rgba(177,151,252,0.18); border-left: 3px solid var(--purple); border-radius: 0 var(--radius) var(--radius) 0; padding: 18px 24px; margin: 16px 0; }
.quote-box .q-text { font-style: italic; color: var(--text-secondary); font-size: 0.92rem; line-height: 1.7; }
.quote-box .q-src { font-size: 0.78rem; color: var(--purple); margin-top: 8px; font-weight: 500; }

.note-box { background: var(--orange-dim); border: 1px solid rgba(255,169,77,0.22); border-radius: var(--radius); padding: 20px 24px; margin: 16px 0; }
.note-box h3 { font-size: 1rem; font-weight: 700; color: var(--orange); margin-bottom: 10px; }
.note-box p { color: var(--text-secondary); }

.method-box { background: var(--blue-dim); border: 1px solid rgba(116,192,252,0.2); border-radius: var(--radius); padding: 24px; margin: 16px 0; }
.method-box h3 { font-size: 1rem; font-weight: 700; color: var(--blue); margin-bottom: 16px; display: flex; align-items: center; gap: 8px; }

/* ─── Tables ─── */
.info-table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 0.88rem; }
.info-table td { padding: 9px 14px; border-bottom: 1px solid var(--border); }
.info-table td:first-child { color: var(--text-muted); font-weight: 500; width: 200px; white-space: nowrap; }
.info-table td:last-child { color: var(--text-secondary); }
.info-table tr.hl td:last-child { color: var(--accent); font-weight: 500; }
.info-table tr.red td:last-child { color: var(--red); font-weight: 600; }
.compare-table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 0.85rem; }
.compare-table th { background: var(--bg-tertiary); color: var(--text-muted); font-weight: 600; font-size: 0.75rem; text-transform: uppercase; letter-spacing: 0.8px; padding: 10px 14px; text-align: left; border-bottom: 1px solid var(--border-light); }
.compare-table td { padding: 10px 14px; border-bottom: 1px solid var(--border); color: var(--text-secondary); }
.compare-table td:first-child { font-weight: 500; color: var(--text-primary); }
.compare-table tr:hover td { background: var(--bg-hover); }

/* ─── KaTeX ─── */
.katex-display { margin: 16px 0; overflow-x: auto; }
.content-section .katex { font-size: 1.05rem; }

.section-divider { display: flex; align-items: center; gap: 16px; margin: 48px 0 28px; font-size: 0.72rem; font-weight: 700; text-transform: uppercase; letter-spacing: 2px; color: var(--text-muted); scroll-margin-top: calc(var(--header-h) + 24px); }
.section-divider::before, .section-divider::after { content: ''; flex: 1; height: 1px; background: linear-gradient(90deg, transparent, var(--border-light), transparent); }

/* ═══════════════════════════════════════════════════════════════
   FLASHCARDS
   ═══════════════════════════════════════════════════════════════ */
.cards-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 16px; margin: 16px 0; }
.flashcard { perspective: 800px; height: 220px; cursor: pointer; }
.flashcard-inner { width: 100%; height: 100%; position: relative; transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1); transform-style: preserve-3d; }
.flashcard.flipped .flashcard-inner { transform: rotateY(180deg); }
.flashcard-front, .flashcard-back { position: absolute; inset: 0; backface-visibility: hidden; border-radius: var(--radius); padding: 20px; display: flex; flex-direction: column; overflow-y: auto; }
.flashcard-front { background: var(--bg-card); border: 1px solid var(--border); }
.flashcard-back { background: var(--green-dim); border: 1px solid rgba(81,207,102,0.25); transform: rotateY(180deg); }
.card-badge { font-size: 0.68rem; font-weight: 700; text-transform: uppercase; letter-spacing: 1px; padding: 3px 10px; border-radius: 4px; align-self: flex-start; margin-bottom: 12px; }
.card-badge.definizione { background: var(--blue-dim); color: var(--blue); }
.card-badge.domanda { background: var(--red-dim); color: var(--red); }
.card-badge.dimostrazione { background: var(--purple-dim); color: var(--purple); }
.card-badge.tranello { background: var(--orange-dim); color: var(--orange); }
.card-badge.risposta { background: rgba(81,207,102,0.15); color: var(--green); }
.card-text { font-size: 0.88rem; line-height: 1.6; color: var(--text-secondary); flex: 1; }
.card-text strong { color: var(--text-primary); }
.card-hint { font-size: 0.72rem; color: var(--text-muted); text-align: center; margin-top: 10px; }

/* ═══════════════════════════════════════════════════════════════
   QUIZ
   ═══════════════════════════════════════════════════════════════ */
.quiz-block { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; margin-bottom: 20px; }
.quiz-block .qb-question { font-size: 1rem; font-weight: 600; color: var(--text-primary); margin-bottom: 16px; line-height: 1.6; }
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-opt { background: var(--bg-tertiary); border: 1px solid var(--border); border-radius: var(--radius-sm); padding: 12px 16px; cursor: pointer; font-size: 0.9rem; color: var(--text-secondary); transition: all var(--transition); display: flex; align-items: flex-start; gap: 10px; }
.quiz-opt:hover:not(.disabled) { border-color: var(--accent-dim); background: var(--accent-glow); color: var(--text-primary); }
.quiz-opt .opt-letter { font-weight: 700; color: var(--text-muted); min-width: 22px; }
.quiz-opt.correct { border-color: var(--green) !important; background: var(--green-dim) !important; color: var(--text-primary); }
.quiz-opt.correct .opt-letter { color: var(--green); }
.quiz-opt.wrong { border-color: var(--red) !important; background: var(--red-dim) !important; color: var(--text-primary); }
.quiz-opt.wrong .opt-letter { color: var(--red); }
.quiz-opt.disabled { cursor: default; opacity: 0.6; }
.quiz-opt.disabled.correct { opacity: 1; }
.quiz-explanation { margin-top: 14px; padding: 14px 18px; background: var(--bg-tertiary); border-radius: var(--radius-sm); border-left: 3px solid var(--green); font-size: 0.88rem; color: var(--text-secondary); line-height: 1.6; display: none; }
.quiz-explanation.show { display: block; }
.quiz-explanation strong { color: var(--text-primary); }
.quiz-score-bar { background: var(--bg-tertiary); border-radius: var(--radius); padding: 16px 20px; margin-top: 20px; display: flex; align-items: center; justify-content: space-between; }
.quiz-score-bar .qs-text { font-size: 0.9rem; color: var(--text-secondary); }
.quiz-score-bar .qs-text strong { color: var(--accent); font-size: 1.1rem; }
.quiz-reset-btn { background: var(--accent); color: #fff; border: none; padding: 8px 18px; border-radius: var(--radius-sm); cursor: pointer; font-family: var(--font-body); font-size: 0.82rem; font-weight: 600; transition: all var(--transition); }
.quiz-reset-btn:hover { filter: brightness(1.15); }

/* ═══════════════════════════════════════════════════════════════
   ANIMATION / VIDEO / GRAPHS
   ═══════════════════════════════════════════════════════════════ */
.anim-container { background: var(--bg-tertiary); border: 1px solid var(--border); border-radius: var(--radius-lg); overflow: hidden; margin: 20px 0; }
.anim-container video, .anim-container img { width: 100%; display: block; }
.anim-caption { padding: 12px 18px; font-size: 0.8rem; color: var(--text-muted); display: flex; align-items: center; gap: 8px; border-top: 1px solid var(--border); }
.anim-caption .anim-badge { background: var(--green-dim); color: var(--green); font-size: 0.68rem; font-weight: 700; padding: 2px 8px; border-radius: 4px; letter-spacing: 0.5px; text-transform: uppercase; }
.anim-placeholder { display: flex; align-items: center; justify-content: center; flex-direction: column; gap: 10px; min-height: 260px; color: var(--text-muted); font-size: 0.88rem; }
.anim-placeholder .anim-ph-icon { font-size: 2.5rem; opacity: 0.4; }
.anim-placeholder .anim-ph-text { font-size: 0.82rem; opacity: 0.6; }

.graph-container { background: var(--bg-tertiary); border: 1px solid var(--border); border-radius: var(--radius-lg); overflow: hidden; margin: 20px 0; }
.graph-container canvas { width: 100%; display: block; }
.graph-controls { padding: 12px 18px; display: flex; align-items: center; gap: 12px; flex-wrap: wrap; border-top: 1px solid var(--border); background: var(--bg-card); }
.graph-slider-group { display: flex; align-items: center; gap: 8px; font-size: 0.8rem; color: var(--text-muted); }
.graph-slider-group input[type="range"] { width: 100px; accent-color: var(--accent); }
.graph-slider-group .slider-val { font-family: var(--font-mono); color: var(--accent); font-size: 0.78rem; min-width: 44px; }
.graph-btn { background: var(--accent-glow); color: var(--accent); border: 1px solid rgba(108,140,255,0.25); border-radius: var(--radius-sm); padding: 5px 14px; font-size: 0.78rem; font-weight: 600; font-family: var(--font-body); cursor: pointer; transition: all var(--transition); }
.graph-btn:hover { background: var(--accent-glow-strong); border-color: var(--accent); }
.graph-caption { padding: 0 18px 12px; font-size: 0.78rem; color: var(--text-muted); display: flex; align-items: center; gap: 8px; }
.graph-caption .interactive-badge { background: var(--teal-dim); color: var(--teal); font-size: 0.68rem; font-weight: 700; padding: 2px 8px; border-radius: 4px; letter-spacing: 0.5px; text-transform: uppercase; }

/* ═══════════════════════════════════════════════════════════════
   FOOTER
   ═══════════════════════════════════════════════════════════════ */
.site-footer { border-top: 1px solid var(--border); padding: 24px 32px; text-align: center; font-size: 0.78rem; color: var(--text-muted); font-weight: 300; }
.site-footer .footer-name { color: var(--accent); font-weight: 600; }
.site-footer .footer-uni { color: var(--text-muted); opacity: 0.7; }
.site-footer-inner { max-width: 960px; margin: 0 auto; display: flex; justify-content: space-between; align-items: center; }
.site-footer-links { display: flex; gap: 20px; }
.site-footer-links a { font-family: var(--font-mono); font-size: 0.75rem; color: var(--text-muted); text-decoration: none; transition: color var(--transition); }
.site-footer-links a:hover { color: var(--text-secondary); }
.site-footer .footer-copy { font-family: var(--font-mono); font-size: 0.75rem; color: var(--text-muted); }
.site-footer-coffee { display: block; text-align: center; padding: 20px 0 0; font-size: 0.8rem; color: var(--text-muted); }
.site-footer-coffee a { color: var(--gold); text-decoration: none; font-weight: 500; transition: color var(--transition); }
.site-footer-coffee a:hover { color: #f5d070; }

/* ═══════════════════════════════════════════════════════════════
   RESPONSIVE
   ═══════════════════════════════════════════════════════════════ */
@media (max-width: 900px) {
  .lesson-sidebar { display: none; }
  .lesson-content { padding: 24px 20px 60px; }
  .page-wrapper { padding: 32px 16px 60px; }
  .hero h1 { font-size: 2rem; }
  .lessons-grid { grid-template-columns: 1fr; }
  .cards-grid { grid-template-columns: 1fr; }
}
@media (max-width: 600px) {
  .hero h1 { font-size: 1.6rem; }
  .lesson-header h1 { font-size: 1.5rem; }
  .formula-item { flex-direction: column; gap: 4px; }
  .formula-label { min-width: unset; }
  .site-footer-inner { flex-direction: column; gap: 12px; text-align: center; }
}

/* ─── Print ─── */
@media print {
  body { overflow: visible; height: auto; background: #fff; color: #000; }
  .lesson-sidebar, .graph-controls, .graph-btn, .card-hint,
  .quiz-options, .quiz-explanation, .quiz-score-bar,
  .section-divider, .theme-toggle { display: none !important; }
  .lesson-layout { display: block; margin-top: 0; height: auto; }
  .lesson-content { max-width: 100%; padding: 0; overflow: visible; }
  .flashcard { height: auto; perspective: none; }
  .flashcard-inner { transform: none !important; transform-style: flat; position: static; }
  .flashcard-front { position: static; backface-visibility: visible; border: 1px solid #ccc; }
  .flashcard-back { display: none; }
  .content-section, .formula-box, .steps-box, .alert-box, .note-box, .quote-box { break-inside: avoid; }
  .formula-box { border: 1px solid #ddd; background: #f9f6ee; }
  .steps-box { border: 1px solid #ddd; background: #f0f6ff; }
  .alert-box { border: 1px solid #ddd; background: #fff0f0; }
  .note-box { border: 1px solid #ddd; background: #fff8f0; }
}