/* ── SHARED MODULE STYLES ── */
:root {
  --bg: #0a0f1e;
  --bg-mid: #111827;
  --bg-card: #161d2e;
  --border: rgba(99,179,237,0.14);
  --accent: #63b3ed;
  --accent-glow: rgba(99,179,237,0.15);
  --green: #22c55e;
  --red: #ef4444;
  --amber: #f59e0b;
  --purple: #a78bfa;
  --text: #e2e8f0;
  --text-muted: #94a3b8;
  --text-faint: #4b5563;
  --white: #f8fafc;
}

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

body {
  font-family: 'DM Sans', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  min-height: 100vh;
}

body::before {
  content: '';
  position: fixed; inset: 0;
  background-image: radial-gradient(rgba(99,179,237,0.06) 1px, transparent 1px);
  background-size: 28px 28px;
  pointer-events: none; z-index: 0;
}

.container { max-width: 980px; margin: 0 auto; padding: 0 24px; position: relative; z-index: 1; }

/* ── NAV ── */
nav {
  position: sticky; top: 0; z-index: 100;
  background: rgba(10,15,30,0.92); backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  padding: 14px 0;
}
.nav-inner { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.nav-brand { font-size: 15px; font-weight: 700; color: var(--accent); text-decoration: none; }
.nav-brand span { color: var(--text-muted); font-weight: 400; }
.nav-links { display: flex; gap: 4px; flex-wrap: wrap; }
.nav-links a {
  padding: 5px 12px; border-radius: 6px; font-size: 13px; font-weight: 500;
  text-decoration: none; color: var(--text-muted); transition: all 0.2s;
}
.nav-links a:hover, .nav-links a.active { color: var(--accent); background: var(--accent-glow); }

/* ── MODULE HEADER ── */
.module-header { padding: 56px 0 36px; border-bottom: 1px solid var(--border); }
.back-link { display: inline-flex; align-items: center; gap: 6px; color: var(--text-muted); text-decoration: none; font-size: 13px; margin-bottom: 20px; transition: color 0.2s; }
.back-link:hover { color: var(--accent); }
.domain-badge {
  display: inline-block; padding: 4px 12px; border-radius: 16px; font-size: 11px; font-weight: 600;
  text-transform: uppercase; letter-spacing: 0.1em; margin-bottom: 14px;
  border: 1px solid var(--mod-color, var(--accent));
  color: var(--mod-color, var(--accent));
  background: color-mix(in srgb, var(--mod-color, var(--accent)) 12%, transparent);
}
.module-header h1 { font-size: clamp(26px, 4vw, 40px); font-weight: 700; color: var(--white); line-height: 1.15; }
.module-header p { font-size: 15px; color: var(--text-muted); margin-top: 10px; max-width: 560px; }

/* ── PROGRESS TRACK ── */
.mod-progress { display: flex; align-items: center; gap: 12px; margin-top: 20px; }
.mod-progress-bar { flex: 1; height: 4px; background: rgba(255,255,255,0.07); border-radius: 4px; overflow: hidden; max-width: 260px; }
.mod-progress-fill { height: 100%; border-radius: 4px; background: var(--mod-color, var(--accent)); transition: width 0.4s; }
.mod-progress-label { font-size: 12px; color: var(--text-faint); font-family: 'JetBrains Mono', monospace; }

/* ── CONCEPT CARDS ── */
.concepts { padding: 48px 0 0; }
.section-label { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.12em; color: var(--text-faint); margin-bottom: 20px; }

.concept-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: 14px; margin-bottom: 20px; overflow: hidden;
  opacity: 0; transform: translateY(20px);
  transition: opacity 0.4s ease, transform 0.4s ease;
}
.concept-card.visible { opacity: 1; transform: translateY(0); }

.concept-header {
  padding: 20px 24px; cursor: pointer; display: flex; align-items: flex-start; gap: 14px;
  transition: background 0.2s;
}
.concept-header:hover { background: rgba(255,255,255,0.03); }

.concept-icon { font-size: 22px; flex-shrink: 0; margin-top: 1px; }
.concept-title-wrap { flex: 1; }
.concept-title { font-size: 16px; font-weight: 600; color: var(--white); }
.concept-subtitle { font-size: 12px; color: var(--text-muted); margin-top: 2px; }
.concept-chevron { color: var(--text-faint); font-size: 14px; transition: transform 0.3s; flex-shrink: 0; margin-top: 3px; }
.concept-card.open .concept-chevron { transform: rotate(180deg); }

.concept-body { padding: 0 24px; max-height: 0; overflow: hidden; transition: max-height 0.4s ease, padding 0.3s; }
.concept-card.open .concept-body { max-height: 1200px; padding: 0 24px 24px; }

.concept-body p { font-size: 14px; color: var(--text-muted); margin-bottom: 14px; line-height: 1.7; }
.concept-body p:last-child { margin-bottom: 0; }
.concept-body strong { color: var(--white); }

/* Visual diagram inside concept */
.diagram {
  background: rgba(13,19,38,0.8); border: 1px solid var(--border);
  border-radius: 10px; padding: 20px; margin: 14px 0;
  font-family: 'JetBrains Mono', monospace; font-size: 12px;
}

/* Comparison table */
.comp-table { width: 100%; border-collapse: collapse; font-size: 13px; margin: 12px 0; }
.comp-table th { padding: 8px 12px; text-align: left; font-size: 11px; font-weight: 600; letter-spacing: 0.08em; text-transform: uppercase; color: var(--text-faint); border-bottom: 1px solid var(--border); }
.comp-table td { padding: 8px 12px; border-bottom: 1px solid rgba(99,179,237,0.05); color: var(--text-muted); }
.comp-table tr:last-child td { border-bottom: none; }
.comp-table td:first-child { color: var(--white); font-weight: 500; }

/* Tag chips */
.tag-wrap { display: flex; flex-wrap: wrap; gap: 7px; margin-top: 10px; }
.tag { padding: 3px 10px; border-radius: 12px; font-size: 12px; font-weight: 500; background: var(--accent-glow); color: var(--accent); border: 1px solid var(--border); }
.tag.red { background: rgba(239,68,68,0.1); color: var(--red); border-color: rgba(239,68,68,0.2); }
.tag.green { background: rgba(34,197,94,0.1); color: var(--green); border-color: rgba(34,197,94,0.2); }
.tag.amber { background: rgba(245,158,11,0.1); color: var(--amber); border-color: rgba(245,158,11,0.2); }
.tag.purple { background: rgba(167,139,250,0.1); color: var(--purple); border-color: rgba(167,139,250,0.2); }

/* Mnemonic box */
.mnemonic {
  padding: 12px 16px; border-radius: 8px; margin: 12px 0;
  background: rgba(167,139,250,0.08); border: 1px solid rgba(167,139,250,0.2);
  font-size: 13px;
}
.mnemonic-label { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.1em; color: var(--purple); margin-bottom: 5px; }

/* ── QUIZ ── */
.quiz-section { padding: 48px 0 80px; }
.quiz-header-row { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 12px; margin-bottom: 28px; }
.quiz-title { font-size: 22px; font-weight: 700; color: var(--white); }
.quiz-counter { font-size: 13px; color: var(--text-muted); font-family: 'JetBrains Mono', monospace; }

.quiz-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: 14px; padding: 28px; margin-bottom: 20px;
  opacity: 0; transform: translateY(16px);
  transition: opacity 0.35s ease, transform 0.35s ease;
}
.quiz-card.visible { opacity: 1; transform: translateY(0); }

.q-num { font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: 0.1em; color: var(--text-faint); margin-bottom: 10px; font-family: 'JetBrains Mono', monospace; }
.q-text { font-size: 16px; font-weight: 500; color: var(--white); margin-bottom: 18px; line-height: 1.5; }

.options { display: flex; flex-direction: column; gap: 10px; }
.opt {
  padding: 12px 16px; border-radius: 9px; border: 1px solid var(--border);
  background: rgba(255,255,255,0.02); cursor: pointer; font-size: 14px;
  color: var(--text); transition: all 0.2s; text-align: left; width: 100%;
  font-family: 'DM Sans', sans-serif;
}
.opt:hover:not(:disabled) { border-color: var(--mod-color, var(--accent)); background: var(--accent-glow); color: var(--white); }
.opt.correct { background: rgba(34,197,94,0.12); border-color: rgba(34,197,94,0.4); color: var(--green); }
.opt.wrong   { background: rgba(239,68,68,0.10); border-color: rgba(239,68,68,0.3);  color: var(--red); }
.opt:disabled { cursor: default; }

.explanation {
  margin-top: 14px; padding: 14px 16px; border-radius: 9px;
  background: rgba(99,179,237,0.07); border: 1px solid var(--border);
  font-size: 13px; color: var(--text-muted); line-height: 1.65;
  display: none;
}
.explanation.show { display: block; }
.explanation strong { color: var(--white); }

/* Score banner */
.score-banner {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: 14px; padding: 32px; text-align: center;
  display: none; margin-top: 28px;
}
.score-banner.show { display: block; }
.score-num { font-size: 52px; font-weight: 700; color: var(--white); font-family: 'JetBrains Mono', monospace; }
.score-num span { color: var(--mod-color, var(--accent)); }
.score-label { font-size: 16px; color: var(--text-muted); margin-top: 6px; }
.score-grade { font-size: 22px; font-weight: 700; margin-top: 12px; }
.score-actions { display: flex; justify-content: center; gap: 12px; flex-wrap: wrap; margin-top: 24px; }

.btn {
  padding: 10px 22px; border-radius: 9px; border: none; cursor: pointer;
  font-size: 14px; font-weight: 600; font-family: 'DM Sans', sans-serif;
  transition: opacity 0.2s;
}
.btn:hover { opacity: 0.85; }
.btn-accent { background: var(--accent); color: #0a0f1e; }
.btn-outline { background: transparent; border: 1px solid var(--border); color: var(--text-muted); }

/* ── FOOTER ── */
footer { padding: 32px 0; border-top: 1px solid var(--border); margin-top: 16px; }
.footer-inner { display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: 12px; }
footer p { font-size: 13px; color: var(--text-faint); }
footer a { color: var(--text-muted); text-decoration: none; }
footer a:hover { color: var(--accent); }

/* Intersection observer fade-in */
.fade-in { opacity: 0; transform: translateY(20px); transition: opacity 0.45s ease, transform 0.45s ease; }
.fade-in.visible { opacity: 1; transform: translateY(0); }

/* ── TTS READ-ALOUD BUTTONS ── */
.tts-btn {
  flex-shrink: 0; width: 36px; height: 36px; border-radius: 50%;
  background: rgba(99,179,237,0.10); border: 1px solid rgba(99,179,237,0.25);
  cursor: pointer; font-size: 16px; display: flex; align-items: center; justify-content: center;
  transition: all 0.25s ease; margin-right: 6px; padding: 0;
}
.tts-btn:hover { background: rgba(99,179,237,0.22); border-color: rgba(99,179,237,0.5); transform: scale(1.08); }
.tts-btn.speaking {
  background: rgba(239,68,68,0.15); border-color: rgba(239,68,68,0.45);
  animation: tts-pulse 1.2s ease-in-out infinite;
}
.tts-quiz-btn {
  width: 30px; height: 30px; border-radius: 50%; float: right; margin: 0 0 8px 8px;
  background: rgba(99,179,237,0.10); border: 1px solid rgba(99,179,237,0.25);
  cursor: pointer; font-size: 14px; display: flex; align-items: center; justify-content: center;
  transition: all 0.25s ease; padding: 0;
}
.tts-quiz-btn:hover { background: rgba(99,179,237,0.22); border-color: rgba(99,179,237,0.5); transform: scale(1.08); }
.tts-quiz-btn.speaking {
  background: rgba(239,68,68,0.15); border-color: rgba(239,68,68,0.45);
  animation: tts-pulse 1.2s ease-in-out infinite;
}
@keyframes tts-pulse {
  0%, 100% { box-shadow: 0 0 0 0 rgba(239,68,68,0.3); }
  50% { box-shadow: 0 0 0 6px rgba(239,68,68,0); }
}