/* OpenMat study site */
:root {
  --bg: #f7f6f3;
  --surface: #ffffff;
  --surface-2: #f2f1ec;
  --text: #1c1917;
  --muted: #6b6256;
  --border: #e5e1d8;
  --primary: #4f46e5;
  --primary-ink: #ffffff;
  --primary-soft: #eef0fe;
  --good: #15803d;
  --good-soft: #e7f6ec;
  --bad: #be123c;
  --bad-soft: #fce8ec;
  --warn: #b45309;
  --warn-soft: #fbf0dd;
  --quant: #4f46e5;
  --verbal: #0d9488;
  --data-insights: #b45309;
  --shadow: 0 1px 2px rgba(28, 25, 23, 0.05), 0 8px 24px rgba(28, 25, 23, 0.06);
  --radius: 14px;
  --maxw: 900px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #16151a;
    --surface: #201f27;
    --surface-2: #2a2933;
    --text: #f0eef4;
    --muted: #a29fb0;
    --border: #34323d;
    --primary: #8b83ff;
    --primary-ink: #16151a;
    --primary-soft: #262338;
    --good: #57d38c;
    --good-soft: #17301f;
    --bad: #ff8098;
    --bad-soft: #331821;
    --warn: #f0b45e;
    --warn-soft: #302614;
    --quant: #8b83ff;
    --verbal: #4fd1c5;
    --data-insights: #f0b45e;
    --shadow: 0 1px 2px rgba(0, 0, 0, 0.3), 0 10px 30px rgba(0, 0, 0, 0.35);
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

/* Header */
.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 14px clamp(16px, 4vw, 40px);
  background: color-mix(in srgb, var(--surface) 85%, transparent);
  backdrop-filter: saturate(1.4) blur(8px);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 20;
  flex-wrap: wrap;
}
.brand { display: inline-flex; align-items: center; gap: 9px; font-weight: 800; font-size: 1.2rem; color: var(--text); }
.brand:hover { text-decoration: none; }
.brand-mark { color: var(--primary); font-size: 1.35rem; }
.site-nav { display: flex; align-items: center; gap: 6px; flex-wrap: wrap; }
.site-nav a {
  padding: 7px 12px;
  border-radius: 9px;
  color: var(--muted);
  font-weight: 600;
  font-size: 0.94rem;
}
.site-nav a:hover { background: var(--surface-2); color: var(--text); text-decoration: none; }
.site-nav a.active { color: var(--text); background: var(--primary-soft); }
.nav-cta { color: var(--primary) !important; }

/* Layout */
.app { max-width: var(--maxw); margin: 0 auto; padding: clamp(20px, 4vw, 40px) clamp(16px, 4vw, 24px) 64px; }
.loading { text-align: center; color: var(--muted); padding: 80px 0; }
.error-box { background: var(--bad-soft); color: var(--bad); border: 1px solid var(--bad); padding: 16px; border-radius: var(--radius); }

/* Hero */
.hero { text-align: center; padding: 24px 0 8px; }
.hero h1 { font-size: clamp(1.9rem, 5vw, 2.9rem); line-height: 1.1; margin: 0 0 14px; letter-spacing: -0.02em; }
.hero .lede { font-size: 1.12rem; color: var(--muted); max-width: 620px; margin: 0 auto 26px; }
.hero-actions { display: flex; gap: 12px; justify-content: center; flex-wrap: wrap; }

.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 11px 20px; border-radius: 11px; font-weight: 700; font-size: 0.98rem;
  border: 1px solid var(--border); background: var(--surface); color: var(--text); cursor: pointer;
  transition: transform 0.05s ease, box-shadow 0.15s ease;
}
.btn:hover { text-decoration: none; box-shadow: var(--shadow); }
.btn:active { transform: translateY(1px); }
.btn.primary { background: var(--primary); color: var(--primary-ink); border-color: transparent; }
.btn.ghost { background: transparent; }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }

/* Stat cards */
.stat-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 14px; margin: 34px 0; }
.stat-card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px; box-shadow: var(--shadow); border-top: 3px solid var(--sec, var(--primary)); }
.stat-card h3 { margin: 0 0 6px; font-size: 1.05rem; }
.stat-card .big { font-size: 2rem; font-weight: 800; line-height: 1; }
.stat-card .sub { color: var(--muted); font-size: 0.9rem; }

.section-quant { --sec: var(--quant); }
.section-verbal { --sec: var(--verbal); }
.section-data-insights { --sec: var(--data-insights); }

/* Section titles */
h2.view-title { font-size: 1.5rem; margin: 8px 0 4px; letter-spacing: -0.01em; }
.view-sub { color: var(--muted); margin: 0 0 22px; }

/* Filters */
.filters { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; margin-bottom: 22px; }
.filters select, .filters input {
  padding: 9px 12px; border-radius: 10px; border: 1px solid var(--border);
  background: var(--surface); color: var(--text); font-size: 0.92rem; font-family: inherit;
}
.filters input { flex: 1; min-width: 160px; }

/* Badges */
.badges { display: inline-flex; gap: 6px; flex-wrap: wrap; }
.badge { font-size: 0.72rem; font-weight: 700; padding: 3px 9px; border-radius: 999px; letter-spacing: 0.02em; text-transform: uppercase; }
.badge.sec { background: color-mix(in srgb, var(--sec) 15%, transparent); color: var(--sec); }
.badge.easy { background: var(--good-soft); color: var(--good); }
.badge.medium { background: var(--warn-soft); color: var(--warn); }
.badge.hard { background: var(--bad-soft); color: var(--bad); }
.badge.verified { background: var(--good-soft); color: var(--good); }
.badge.in-review { background: var(--warn-soft); color: var(--warn); }
.badge.draft { background: var(--surface-2); color: var(--muted); }
.badge.plain { background: var(--surface-2); color: var(--muted); text-transform: none; letter-spacing: 0; }

/* Card */
.card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: var(--shadow); padding: clamp(18px, 3vw, 28px); margin-bottom: 18px; }
.card-meta { display: flex; justify-content: space-between; align-items: center; gap: 12px; margin-bottom: 14px; flex-wrap: wrap; }
.card .prose { font-size: 1.02rem; }
.prose p:first-child { margin-top: 0; }
.prose p:last-child { margin-bottom: 0; }
.prose code { background: var(--surface-2); padding: 1px 6px; border-radius: 6px; font-size: 0.9em; }

/* Practice */
.practice-progress { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 18px; color: var(--muted); font-size: 0.92rem; flex-wrap: wrap; }
.scorepill { background: var(--surface-2); border-radius: 999px; padding: 5px 14px; font-weight: 700; color: var(--text); }
.choices { list-style: none; margin: 20px 0 0; padding: 0; display: grid; gap: 10px; }
.choice {
  display: flex; gap: 12px; align-items: flex-start; text-align: left; width: 100%;
  padding: 13px 16px; border-radius: 12px; border: 1.5px solid var(--border);
  background: var(--surface); color: var(--text); cursor: pointer; font: inherit; font-size: 1rem;
  transition: border-color 0.12s ease, background 0.12s ease;
}
.choice:hover:not(:disabled) { border-color: var(--primary); background: var(--primary-soft); }
.choice .letter { font-weight: 800; color: var(--muted); min-width: 1.2em; }
.choice.selected { border-color: var(--primary); background: var(--primary-soft); }
.choice.correct { border-color: var(--good); background: var(--good-soft); }
.choice.correct .letter { color: var(--good); }
.choice.wrong { border-color: var(--bad); background: var(--bad-soft); }
.choice.wrong .letter { color: var(--bad); }
.choice:disabled { cursor: default; }

.verdict { margin-top: 20px; padding: 14px 16px; border-radius: 12px; font-weight: 600; }
.verdict.correct { background: var(--good-soft); color: var(--good); }
.verdict.wrong { background: var(--bad-soft); color: var(--bad); }

.reveal { margin-top: 18px; border-top: 1px solid var(--border); padding-top: 18px; }
.reveal h4 { margin: 0 0 8px; font-size: 0.95rem; text-transform: uppercase; letter-spacing: 0.04em; color: var(--muted); }
.hint-list { margin: 0; padding-left: 20px; color: var(--text); }
details.hints { margin-top: 16px; }
details.hints summary { cursor: pointer; font-weight: 700; color: var(--primary); }
.action-row { display: flex; gap: 10px; margin-top: 22px; flex-wrap: wrap; }

/* List rows (browse/lessons) */
.row { background: var(--surface); border: 1px solid var(--border); border-radius: 12px; box-shadow: var(--shadow); margin-bottom: 12px; overflow: hidden; }
.row-head { display: flex; align-items: center; justify-content: space-between; gap: 12px; padding: 15px 18px; cursor: pointer; }
.row-head:hover { background: var(--surface-2); }
.row-title { font-weight: 600; }
.row-body { padding: 0 18px 18px; display: none; }
.row.open .row-body { display: block; }
.row-body .prose { border-top: 1px solid var(--border); padding-top: 14px; }
.empty { color: var(--muted); text-align: center; padding: 40px 0; }

/* Lesson reader */
.lesson-body h2 { font-size: 1.25rem; margin-top: 28px; }
.lesson-body h3 { font-size: 1.05rem; }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }

/* About */
.prose-page { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: var(--shadow); padding: clamp(20px, 4vw, 36px); }
.prose-page h2 { margin-top: 28px; }
.prose-page h2:first-child { margin-top: 0; }
.prose-page ul { padding-left: 22px; }

/* Footer */
.site-footer { border-top: 1px solid var(--border); padding: 28px clamp(16px, 4vw, 40px); color: var(--muted); font-size: 0.9rem; text-align: center; }
.site-footer p { margin: 4px 0; }
.disclaimer { font-size: 0.82rem; opacity: 0.8; }

@media (max-width: 560px) {
  .site-header { gap: 8px; }
  .brand-name { font-size: 1.05rem; }
  .site-nav a { padding: 6px 9px; font-size: 0.88rem; }
}