/* ============================================================
   Velnov - study notes & formula pages (generated by tools/build-pages.js)
   Same brand colours as css/style.css; light + dark via the OS setting.
   ============================================================ */

:root {
  --primary: #6366f1;
  --primary-dark: #4f46e5;
  --grad: linear-gradient(135deg, #6366f1 0%, #8b5cf6 55%, #a855f7 100%);
  --bg: #f4f5fb;
  --card: #ffffff;
  --inset: #f7f8fc;
  --text: #101426;
  --muted: #5f6787;
  --border: #e7e9f3;
  --good: #047857;
  --good-bg: #ecfdf5;
  --code-bg: #0e1222;
  --code-text: #dfe4f4;
  --font-sans: 'Inter', system-ui, 'Segoe UI', sans-serif;
  --font-display: 'Sora', 'Inter', system-ui, sans-serif;
  --font-mono: 'JetBrains Mono', Consolas, 'Cascadia Code', monospace;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b0e1a;
    --card: #141829;
    --inset: #1a1f33;
    --text: #e8eaf6;
    --muted: #a0a7c4;
    --border: #262b45;
    --good: #6ee7b7;
    --good-bg: rgba(16, 185, 129, 0.12);
  }
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body { font-family: var(--font-sans); background: var(--bg); color: var(--text); line-height: 1.7; -webkit-font-smoothing: antialiased; }
a { color: var(--primary-dark); }
@media (prefers-color-scheme: dark) { a { color: #a5b4fc; } }
.wrap { max-width: 880px; margin: 0 auto; padding: 0 16px; }

/* header / footer */
.site-head { background: var(--card); border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 10; }
.head-inner { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; min-height: 60px; padding-top: 8px; padding-bottom: 8px; }
.brand { font-family: var(--font-display); font-weight: 800; font-size: 1.3rem; color: var(--text); text-decoration: none; }
.brand span { background: var(--grad); -webkit-background-clip: text; background-clip: text; color: transparent; }
.site-head nav { display: flex; gap: 16px; flex-wrap: wrap; }
.site-head nav a { color: var(--text); text-decoration: none; font-weight: 600; font-size: 0.92rem; }
.site-head nav a:hover { color: var(--primary); }
.site-foot { margin-top: 56px; padding: 28px 0; border-top: 1px solid var(--border); color: var(--muted); font-size: 0.9rem; text-align: center; }
.site-foot p + p { margin-top: 6px; }

/* page header */
main.wrap { padding-top: 20px; }
.crumbs { font-size: 0.85rem; color: var(--muted); margin-bottom: 18px; }
.crumbs a { color: var(--muted); }
.page-head { margin-bottom: 24px; }
.kicker { font-size: 0.85rem; font-weight: 700; color: var(--primary); letter-spacing: 0.02em; }
h1 { font-family: var(--font-display); font-size: clamp(1.6rem, 4.5vw, 2.3rem); line-height: 1.2; margin: 6px 0 12px; }
h2 { font-family: var(--font-display); font-size: 1.35rem; line-height: 1.3; margin: 36px 0 14px; scroll-margin-top: 80px; }
h3 { font-size: 1.08rem; line-height: 1.4; }
.lead { font-size: 1.06rem; color: var(--muted); }
.meta { margin-top: 10px; font-size: 0.9rem; color: var(--muted); }
.jump { font-size: 0.92rem; color: var(--muted); margin: 10px 0; }

.box { background: var(--card); border: 1px solid var(--border); border-radius: 16px; padding: 16px 20px; }
.box h2 { margin-top: 0; font-size: 1.1rem; }

/* tags & badges */
.tags { display: flex; flex-wrap: wrap; gap: 6px; }
.tags span { font-size: 0.8rem; background: var(--inset); border: 1px solid var(--border); border-radius: 999px; padding: 2px 10px; color: var(--muted); }
.badge { display: inline-block; font-size: 0.72rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.04em; border-radius: 999px; padding: 1px 9px; background: var(--inset); color: var(--muted); vertical-align: middle; }
.badge-easy { background: #dcfce7; color: #166534; }
.badge-medium { background: #fef3c7; color: #92400e; }
.badge-hard { background: #fee2e2; color: #991b1b; }

/* topic overview (hand-written study notes, from data/notes/) */
.overview { background: var(--card); border: 1px solid var(--border); border-left: 4px solid var(--primary); border-radius: 16px; padding: 18px 22px 20px; margin-bottom: 20px; scroll-margin-top: 80px; }
.ov-kicker { font-size: 0.78rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.06em; color: var(--primary); }
.overview h2 { margin: 2px 0 8px; }
.overview h3 { font-family: var(--font-display); font-size: 1.15rem; margin: 28px 0 0; padding-top: 16px; border-top: 1px solid var(--border); scroll-margin-top: 80px; }
.overview h4 { font-size: 1rem; margin: 18px 0 0; }
.overview p, .overview ul, .overview ol, .overview dl, .overview table, .overview .ov-eg { margin-top: 8px; }
.overview .ov-eg p, .overview .ov-eg ul, .overview li p { margin-top: 0; }
.overview .ov-intro { font-size: 1.04rem; }
.ov-toc { margin-top: 10px; font-size: 0.88rem; color: var(--muted); }
.ov-list, .ov-eg ul, .ov-quiz { padding-left: 22px; }
.ov-list li + li, .ov-eg li + li { margin-top: 4px; }
.ov-eg { background: var(--inset); border-radius: 10px; padding: 8px 12px; }
.ov-remember { background: rgba(245, 158, 11, 0.1); border-left: 3px solid #f59e0b; border-radius: 0 10px 10px 0; padding: 8px 12px; }
.ov-key { background: var(--inset); border: 1px dashed var(--border); border-radius: 10px; padding: 8px 12px; text-align: center; font-weight: 700; }
.ov-table { width: 100%; border-collapse: collapse; font-size: 0.93rem; }
.ov-table th, .ov-table td { border: 1px solid var(--border); padding: 8px 10px; text-align: left; vertical-align: top; }
.ov-table th { background: var(--inset); }
.ov-table td:first-child::before { content: "✗ "; color: #dc2626; font-weight: 700; }
.ov-table td:last-child::before { content: "✓ "; color: var(--good); font-weight: 700; }
.terms { display: grid; gap: 8px; }
.terms div { background: var(--inset); border: 1px solid var(--border); border-radius: 10px; padding: 8px 12px; }
.terms dt { font-weight: 700; }
.terms dd { color: var(--muted); font-size: 0.95rem; }
.ov-quiz li + li { margin-top: 10px; }
.ov-quiz summary { cursor: pointer; font-size: 0.88rem; font-weight: 600; color: var(--primary-dark); }
@media (prefers-color-scheme: dark) { .ov-quiz summary { color: #a5b4fc; } }
.ov-quiz details p { margin-top: 4px; color: var(--good); }
.ov-takeaway { background: var(--good-bg); border: 1px solid var(--good); border-radius: 12px; padding: 10px 14px; margin-top: 24px !important; }
.ov-foot { margin-top: 16px; font-size: 0.85rem; color: var(--muted); }
.overview pre.code { margin: 8px 0 0; }
.ov-out { margin-top: 4px; background: var(--inset); border: 1px solid var(--border); border-radius: 10px; padding: 8px 14px; font-family: var(--font-mono); font-size: 0.85rem; line-height: 1.5; white-space: pre-wrap; overflow-x: auto; }
.ov-out span { display: block; font-family: var(--font-sans); font-size: 0.72rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.05em; color: var(--muted); }
code.ic { font-family: var(--font-mono); font-size: 0.88em; background: var(--inset); border: 1px solid var(--border); border-radius: 5px; padding: 0 4px; }

/* questions */
.q { background: var(--card); border: 1px solid var(--border); border-radius: 16px; padding: 18px 20px; margin-bottom: 14px; scroll-margin-top: 80px; }
.q-head { display: flex; align-items: center; gap: 8px; font-weight: 700; color: var(--muted); font-size: 0.9rem; }
.q-text { font-weight: 600; font-size: 1.04rem; margin: 8px 0 10px; white-space: pre-wrap; }
.opts { list-style: none; display: grid; gap: 6px; }
.opts li { border: 1px solid var(--border); border-radius: 10px; padding: 7px 12px; background: var(--inset); }
.opts li.correct { border-color: var(--good); background: var(--good-bg); }
.opt-key { display: inline-block; min-width: 1.4em; font-weight: 700; color: var(--primary); }
.opts li.correct .opt-key { color: var(--good); }
.ans { margin-top: 12px; padding-top: 12px; border-top: 1px dashed var(--border); }
.ans > * + * { margin-top: 8px; }
.expl { white-space: pre-wrap; }
.notes { padding-left: 20px; color: var(--muted); font-size: 0.95rem; }
pre.code { background: var(--code-bg); color: var(--code-text); border-radius: 10px; padding: 12px 14px; overflow-x: auto; font-family: var(--font-mono); font-size: 0.88rem; line-height: 1.55; margin: 6px 0 12px; }

/* formulas */
.formula { background: var(--card); border: 1px solid var(--border); border-radius: 16px; padding: 18px 20px; margin-bottom: 14px; }
.formula > * + * { margin-top: 8px; }
.f-eq { font-family: var(--font-mono); font-size: 1.08rem; background: var(--inset); border-radius: 10px; padding: 10px 14px; overflow-x: auto; white-space: pre-wrap; }
.sym { border-collapse: collapse; font-size: 0.92rem; }
.sym th { text-align: left; padding: 3px 14px 3px 0; font-family: var(--font-mono); white-space: nowrap; vertical-align: top; }
.sym td { padding: 3px 0; color: var(--muted); }
.eg code { font-family: var(--font-mono); white-space: pre-wrap; }

/* lists & grids */
.topic-list { list-style: none; counter-reset: t; display: grid; gap: 10px; }
.topic-list a { display: flex; flex-direction: column; background: var(--card); border: 1px solid var(--border); border-radius: 14px; padding: 14px 18px; text-decoration: none; color: var(--text); }
.topic-list a:hover { border-color: var(--primary); }
.topic-list span { font-size: 0.88rem; color: var(--muted); }
.subject-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 14px; }
.subject-card { display: flex; flex-direction: column; gap: 4px; background: var(--card); border: 1px solid var(--border); border-top: 4px solid var(--accent, var(--primary)); border-radius: 16px; padding: 16px 18px; text-decoration: none; color: var(--text); }
.subject-card:hover { box-shadow: 0 10px 24px -12px rgba(60, 45, 120, 0.35); }
.subject-card .ico { font-size: 1.6rem; }
.subject-card span { color: var(--muted); font-size: 0.92rem; }
.subject-card .small { font-size: 0.82rem; }

.pager { display: flex; justify-content: space-between; gap: 12px; margin-top: 28px; font-weight: 600; }
.cta { margin-top: 20px; text-align: center; }
.btn { display: inline-block; background: var(--grad); color: #fff !important; text-decoration: none; font-weight: 700; padding: 11px 22px; border-radius: 12px; }

/* AdSense auto ads: keep them from squeezing the text column */
ins.adsbygoogle { margin: 16px auto; }