:root {
  --bg: #0f1419;
  --surface: #1a2332;
  --surface2: #243044;
  --text: #e8eef7;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent2: #a78bfa;
  --success: #4ade80;
  --warn: #fbbf24;
  --danger: #f87171;
  --border: rgba(148, 163, 184, 0.15);
  --radius: 12px;
  --font: "SF Pro Text", "Segoe UI", system-ui, sans-serif;
  --mono: "SF Mono", "JetBrains Mono", monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  display: grid;
  grid-template-columns: 280px 1fr;
  min-height: 100vh;
  line-height: 1.55;
}

.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  padding: 1.5rem 1rem;
  background: linear-gradient(180deg, #121a26 0%, #0f1419 100%);
  border-right: 1px solid var(--border);
}
.brand-tag {
  display: inline-block;
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.35rem;
}
.brand h1 { margin: 0; font-size: 1.35rem; }
.exam-date { color: var(--warn); font-size: 0.85rem; margin: 0.5rem 0 1rem; }
.sidebar nav { display: flex; flex-direction: column; gap: 0.25rem; }
.sidebar nav a {
  color: var(--muted);
  text-decoration: none;
  padding: 0.45rem 0.65rem;
  border-radius: 8px;
  font-size: 0.9rem;
}
.sidebar nav a:hover { background: var(--surface2); color: var(--text); }
.sidebar-note { font-size: 0.75rem; color: var(--muted); margin-top: 1.5rem; }

main { padding: 1.5rem 2rem 4rem; max-width: 980px; }

.hero {
  display: flex;
  justify-content: space-between;
  gap: 1.5rem;
  align-items: flex-start;
  margin-bottom: 1.5rem;
  padding: 1.5rem;
  background: linear-gradient(135deg, rgba(56,189,248,0.12), rgba(167,139,250,0.1));
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.eyebrow { color: var(--accent); font-size: 0.8rem; margin: 0 0 0.35rem; }
.hero h2 { margin: 0 0 0.5rem; font-size: 1.45rem; line-height: 1.25; }
.hero-sub { color: var(--muted); margin: 0; font-size: 0.95rem; }
.hero-stats {
  display: flex;
  gap: 1rem;
  flex-shrink: 0;
}
.hero-stats div {
  text-align: center;
  background: var(--surface);
  padding: 0.75rem 1rem;
  border-radius: 10px;
  border: 1px solid var(--border);
}
.hero-stats strong { display: block; font-size: 1.4rem; color: var(--accent); }
.hero-stats span { font-size: 0.75rem; color: var(--muted); text-transform: uppercase; letter-spacing: 0.05em; }

.panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  margin-bottom: 1.25rem;
}
.panel h3 {
  margin: 0 0 1rem;
  font-size: 1.15rem;
  color: var(--accent);
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.5rem;
}
.panel h4 { margin: 0 0 0.5rem; font-size: 0.95rem; }

.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 1.25rem; }
@media (max-width: 900px) {
  body { grid-template-columns: 1fr; }
  .sidebar { position: relative; height: auto; }
  .grid-2 { grid-template-columns: 1fr; }
  .hero { flex-direction: column; }
}

.checklist { margin: 0; padding-left: 1.1rem; }
.checklist li { margin-bottom: 0.35rem; }

.data-table { width: 100%; border-collapse: collapse; font-size: 0.88rem; }
.data-table th, .data-table td {
  border: 1px solid var(--border);
  padding: 0.45rem 0.6rem;
  text-align: left;
}
.data-table th { background: var(--surface2); color: var(--accent); }
.hint { font-size: 0.85rem; color: var(--warn); margin-top: 0.75rem; }

.topic-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 0.75rem;
}
.topic-cards article {
  background: var(--surface2);
  padding: 0.85rem;
  border-radius: 10px;
  border: 1px solid var(--border);
}
.topic-cards h4 { color: var(--accent2); margin-bottom: 0.35rem; }
.topic-cards p { margin: 0; font-size: 0.85rem; color: var(--muted); }

.formula-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 0.65rem;
}
.formula-card {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.65rem 0.85rem;
  font-size: 0.92rem;
  overflow-x: auto;
}
.formula-card .formula-tex {
  line-height: 1.8;
}
.formula-card .katex {
  font-size: 1em;
}
.formula-card .label {
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--accent2);
  margin-bottom: 0.25rem;
}

.content-block { font-size: 0.95rem; }
.content-block ul { padding-left: 1.2rem; }
.center-math { text-align: center; margin: 0.75rem 0; }

.problem {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
  margin-bottom: 0.75rem;
  overflow: hidden;
}
.problem-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  cursor: pointer;
  gap: 1rem;
}
.problem-header:hover { background: rgba(56,189,248,0.06); }
.problem-tag {
  font-size: 0.7rem;
  background: rgba(167,139,250,0.2);
  color: var(--accent2);
  padding: 0.15rem 0.45rem;
  border-radius: 999px;
  white-space: nowrap;
}
.problem-body {
  display: none;
  padding: 0 1rem 1rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
}
.problem.open .problem-body { display: block; }
.problem-steps { margin-top: 0.5rem; }
.problem-steps li { margin-bottom: 0.35rem; }

.test-tabs { display: flex; gap: 0.5rem; margin-bottom: 1rem; flex-wrap: wrap; }
.test-tab {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 0.5rem 1rem;
  border-radius: 999px;
  cursor: pointer;
  font: inherit;
}
.test-tab.active { background: var(--accent); color: #0f1419; border-color: var(--accent); font-weight: 600; }

.quiz-q {
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
  margin-bottom: 0.75rem;
}
.quiz-q.correct { border-color: var(--success); }
.quiz-q.wrong { border-color: var(--danger); }
.quiz-options { display: flex; flex-direction: column; gap: 0.35rem; margin-top: 0.65rem; }
.quiz-options label {
  display: flex;
  align-items: flex-start;
  gap: 0.5rem;
  padding: 0.45rem 0.6rem;
  border-radius: 8px;
  cursor: pointer;
  border: 1px solid transparent;
}
.quiz-options label:hover { background: rgba(255,255,255,0.04); }
.quiz-options input { margin-top: 0.2rem; }
.explanation {
  margin-top: 0.65rem;
  padding: 0.65rem;
  background: rgba(56,189,248,0.08);
  border-radius: 8px;
  font-size: 0.88rem;
  display: none;
}
.quiz-q.answered .explanation { display: block; }

.test-score {
  margin-top: 1rem;
  padding: 0.85rem 1rem;
  background: var(--surface2);
  border-radius: 10px;
  font-weight: 600;
}

.sources ul { margin: 0; padding-left: 1.2rem; color: var(--muted); font-size: 0.9rem; }
.sources li { margin-bottom: 0.35rem; }

.katex { font-size: 1.05em; }

/* Pronunciation guide */
.pronounce-panel h3 { color: var(--warn); }
.section-lead { color: var(--muted); margin: -0.5rem 0 1rem; font-size: 0.92rem; }
.pronounce-toolbar { margin-bottom: 1rem; }
.pronounce-lang-toggle {
  display: flex;
  gap: 0.35rem;
  margin-bottom: 0.65rem;
}
.pron-lang {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--muted);
  padding: 0.35rem 0.85rem;
  border-radius: 8px;
  font-size: 0.85rem;
  cursor: pointer;
  font: inherit;
}
.pron-lang.active {
  background: var(--warn);
  color: #0f1419;
  border-color: var(--warn);
  font-weight: 600;
}
.pronounce-toolbar input {
  width: 100%;
  max-width: 420px;
  padding: 0.55rem 0.85rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--surface2);
  color: var(--text);
  font: inherit;
}
.pronounce-filters {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin-top: 0.65rem;
}
.pron-filter {
  background: var(--surface2);
  border: 1px solid var(--border);
  color: var(--muted);
  padding: 0.3rem 0.65rem;
  border-radius: 999px;
  font-size: 0.78rem;
  cursor: pointer;
  font: inherit;
}
.pron-filter.active { background: var(--warn); color: #0f1419; border-color: var(--warn); font-weight: 600; }
.pronounce-intro, .pronounce-agreement {
  font-size: 0.9rem;
  color: var(--muted);
  margin-bottom: 1rem;
  padding: 0.75rem 1rem;
  background: rgba(251, 191, 36, 0.08);
  border-radius: 8px;
  border-left: 3px solid var(--warn);
}
.pronounce-category { margin-bottom: 1.5rem; }
.pronounce-category h4 {
  color: var(--accent2);
  margin: 0 0 0.5rem;
  font-size: 0.95rem;
}
.pronounce-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.88rem;
}
.pronounce-table th, .pronounce-table td {
  border: 1px solid var(--border);
  padding: 0.45rem 0.65rem;
  text-align: left;
  vertical-align: top;
}
.pronounce-table th { background: var(--surface2); color: var(--accent); font-size: 0.78rem; }
.sym-cell code {
  font-family: var(--mono);
  color: var(--accent);
  font-size: 0.9rem;
  white-space: nowrap;
}
.say-cell { color: var(--text); font-weight: 500; }
.tip-cell { color: var(--muted); font-size: 0.82rem; }
.pronounce-phrases h4 { color: var(--accent2); margin: 1.5rem 0 0.75rem; }
.phrase-cards { display: flex; flex-direction: column; gap: 0.5rem; }
.phrase-card {
  display: grid;
  grid-template-columns: 1fr auto 1.5fr;
  gap: 0.75rem;
  align-items: center;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.65rem 0.85rem;
  font-size: 0.88rem;
}
.phrase-expr { font-family: var(--mono); color: var(--accent); word-break: break-all; }
.phrase-arrow { color: var(--muted); }
.phrase-say { color: var(--text); }
@media (max-width: 700px) {
  .phrase-card { grid-template-columns: 1fr; gap: 0.25rem; }
  .phrase-arrow { display: none; }
}