:root {
  --ink: #16202c;
  --ink-soft: #465666;
  --ink-faint: #6b7c8d;
  --line: #dde5ee;
  --line-soft: #eaf0f7;
  --bg: #fbfcfe;
  --paper: #ffffff;
  --brand: #2563eb;
  --brand-dark: #1d4ed8;
  --brand-wash: #eef4ff;
  --warn-bg: #fff8ed;
  --warn-line: #f0c987;
  --warn-ink: #7a4a07;
  --ok-bg: #f0f8f3;
  --ok-line: #b7ddc5;
  --ok-ink: #1f5c3b;
  --radius: 10px;
  --max: 1080px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--brand); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 3px; }

.wrap {
  width: 100%;
  max-width: var(--max);
  margin: 0 auto;
  padding: 0 20px;
}

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  background: var(--brand);
  color: #fff;
  padding: 10px 16px;
  z-index: 100;
}
.skip-link:focus { left: 12px; top: 12px; }

/* ---------- header ---------- */
.site-header {
  background: rgba(251, 252, 254, 0.94);
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 20;
  backdrop-filter: saturate(180%) blur(8px);
}
.header-inner {
  display: flex;
  align-items: center;
  gap: 20px;
  min-height: 62px;
  flex-wrap: wrap;
}
.brand {
  display: flex;
  align-items: baseline;
  gap: 8px;
  color: var(--ink);
  font-weight: 700;
  font-size: 19px;
  letter-spacing: 0.02em;
}
.brand:hover { text-decoration: none; }
.brand span.brand-sub {
  font-size: 12px;
  font-weight: 500;
  color: var(--ink-faint);
  letter-spacing: 0;
}
.site-nav {
  margin-left: auto;
  display: flex;
  flex-wrap: wrap;
  gap: 4px 16px;
  font-size: 14.5px;
}
.site-nav a {
  color: var(--ink-soft);
  padding: 6px 0;
  border-bottom: 2px solid transparent;
}
.site-nav a:hover { color: var(--brand); text-decoration: none; }
.site-nav a[aria-current="page"] {
  color: var(--brand);
  border-bottom-color: var(--brand);
  font-weight: 600;
}

/* ---------- main ---------- */
main { padding: 40px 0 56px; }

h1 {
  font-size: 30px;
  line-height: 1.4;
  letter-spacing: -0.01em;
  margin: 0 0 14px;
}
h2 {
  font-size: 21px;
  line-height: 1.5;
  margin: 42px 0 12px;
  padding-top: 8px;
}
h3 {
  font-size: 17px;
  margin: 26px 0 8px;
}
p { margin: 0 0 14px; }

.eyebrow {
  font-size: 12.5px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--brand);
  font-weight: 700;
  margin: 0 0 10px;
}

.lede {
  font-size: 18px;
  line-height: 1.8;
  color: var(--ink-soft);
  border-left: 3px solid var(--brand);
  padding: 2px 0 2px 18px;
  margin: 0 0 8px;
}
.lede strong { color: var(--ink); }

.definition {
  background: var(--paper);
  border: 1px solid var(--line);
  border-left: 4px solid var(--brand);
  border-radius: var(--radius);
  padding: 20px 22px;
  margin: 22px 0 8px;
}
.definition p { margin: 0; font-size: 16.5px; }
.definition .label {
  display: block;
  font-size: 12px;
  letter-spacing: 0.1em;
  color: var(--brand);
  font-weight: 700;
  margin-bottom: 6px;
}

.meta-line {
  font-size: 13px;
  color: var(--ink-faint);
  margin: 0 0 26px;
}

ul, ol { margin: 0 0 16px; padding-left: 22px; }
li { margin: 0 0 8px; }

/* ---------- components ---------- */
.grid {
  display: grid;
  gap: 16px;
  margin: 18px 0 8px;
}
.grid.cols-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid.cols-3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }

.card {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px 20px;
}
.card h3 { margin-top: 0; }
.card p:last-child { margin-bottom: 0; }
.card .num {
  font-size: 12px;
  font-weight: 700;
  color: var(--brand);
  letter-spacing: 0.1em;
  display: block;
  margin-bottom: 4px;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0 22px;
  font-size: 14.5px;
  background: var(--paper);
}
caption {
  text-align: left;
  font-size: 13px;
  color: var(--ink-faint);
  padding-bottom: 8px;
}
th, td {
  border: 1px solid var(--line);
  padding: 10px 12px;
  text-align: left;
  vertical-align: top;
}
th {
  background: var(--brand-wash);
  font-weight: 600;
  color: var(--ink);
  white-space: nowrap;
}
tbody tr:nth-child(even) { background: #fafcff; }

.table-scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; }
.table-scroll table { min-width: 620px; }

.note {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--brand-wash);
  padding: 14px 18px;
  margin: 20px 0;
  font-size: 14.5px;
}
.note.warn {
  background: var(--warn-bg);
  border-color: var(--warn-line);
  color: var(--warn-ink);
}
.note.ok {
  background: var(--ok-bg);
  border-color: var(--ok-line);
  color: var(--ok-ink);
}
.note p:last-child { margin-bottom: 0; }
.note strong { color: inherit; }

.ref {
  font-size: 12px;
  vertical-align: super;
  line-height: 0;
  margin-left: 2px;
  white-space: nowrap;
}
.ref a { color: var(--brand); font-weight: 600; }

.badge {
  display: inline-block;
  font-size: 12px;
  line-height: 1.6;
  padding: 1px 8px;
  border-radius: 999px;
  border: 1px solid var(--line);
  color: var(--ink-soft);
  background: #fff;
  white-space: nowrap;
}
.badge.blue { color: var(--brand-dark); border-color: #c3d6fb; background: var(--brand-wash); }
.badge.gray { color: var(--ink-faint); }

.faq-item {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 18px 20px;
  margin: 0 0 12px;
}
.faq-item h3 { margin: 0 0 8px; font-size: 16.5px; }
.faq-item p:last-child { margin-bottom: 0; }

figure {
  margin: 22px 0;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px;
}
figure img {
  display: block;
  width: 100%;
  height: auto;
  border-radius: 6px;
  border: 1px solid var(--line-soft);
}
figcaption {
  font-size: 13px;
  color: var(--ink-faint);
  padding: 10px 4px 0;
}

.toc {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 22px;
  margin: 24px 0;
  font-size: 14.5px;
}
.toc p { margin: 0 0 6px; font-weight: 600; font-size: 13px; color: var(--ink-faint); letter-spacing: 0.08em; }
.toc ul { margin: 0; padding-left: 20px; }
.toc li { margin-bottom: 4px; }

.src-list { counter-reset: src; list-style: none; padding-left: 0; }
.src-list > li {
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin-bottom: 12px;
  scroll-margin-top: 80px;
}
.src-list .src-id {
  display: inline-block;
  font-size: 12px;
  font-weight: 700;
  color: #fff;
  background: var(--brand);
  border-radius: 4px;
  padding: 0 7px;
  margin-right: 8px;
  vertical-align: 1px;
}
.src-list code {
  font-size: 13px;
  background: #f3f6fa;
  border: 1px solid var(--line-soft);
  border-radius: 4px;
  padding: 1px 5px;
  word-break: break-all;
}
.src-list p:last-child { margin-bottom: 0; }

.entry-links {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 24px 0 6px;
}
.btn {
  display: inline-block;
  padding: 10px 18px;
  border-radius: 8px;
  font-size: 14.5px;
  font-weight: 600;
  border: 1px solid var(--brand);
  background: var(--brand);
  color: #fff;
}
.btn:hover { background: var(--brand-dark); text-decoration: none; }
.btn.ghost { background: #fff; color: var(--brand); }
.btn.ghost:hover { background: var(--brand-wash); text-decoration: none; }

/* ---------- footer ---------- */
.site-footer {
  border-top: 1px solid var(--line);
  background: #fff;
  padding: 34px 0 40px;
  font-size: 13.5px;
  color: var(--ink-faint);
}
.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr;
  gap: 28px;
}
.footer-grid h2 {
  font-size: 13px;
  letter-spacing: 0.08em;
  color: var(--ink-soft);
  margin: 0 0 10px;
  padding: 0;
}
.footer-grid ul { list-style: none; padding: 0; margin: 0; }
.footer-grid li { margin-bottom: 6px; }
.footer-grid a { color: var(--ink-soft); }
.footer-bottom {
  margin-top: 26px;
  padding-top: 18px;
  border-top: 1px solid var(--line-soft);
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  justify-content: space-between;
}
.footer-bottom p { margin: 0; }

@media (max-width: 760px) {
  body { font-size: 15.5px; }
  main { padding: 28px 0 40px; }
  h1 { font-size: 24px; }
  h2 { font-size: 19px; margin-top: 34px; }
  .lede { font-size: 16.5px; padding-left: 14px; }
  .grid.cols-2, .grid.cols-3 { grid-template-columns: 1fr; }
  .header-inner { min-height: 56px; gap: 10px; }
  .site-nav { margin-left: 0; width: 100%; gap: 4px 14px; font-size: 14px; padding-bottom: 4px; }
  .footer-grid { grid-template-columns: 1fr; gap: 20px; }
  .definition { padding: 16px 18px; }
  .card { padding: 16px 16px; }
}