/* When2Buy — Options Data Standard
   Design: quiet fintech/reference-doc aesthetic. No gradients, no glow,
   one accent color, generous whitespace, data-dense tables done cleanly. */

:root {
  --ink: #14181f;
  --ink-soft: #454e5c;
  --ink-faint: #6b7484;
  --paper: #ffffff;
  --paper-sunk: #f4f6f8;
  --paper-card: #fbfbfc;
  --line: #dde1e7;
  --line-soft: #eceef1;
  --accent: #0b5e59;
  --accent-ink: #ffffff;
  --accent-soft: #e3f0ee;
  --p0: #9a3412;
  --p0-bg: #fdf1ea;
  --p1: #8a6d00;
  --p1-bg: #fbf5df;
  --p2: #3a4a63;
  --p2-bg: #eef1f6;
  --code-bg: #eef1f4;
  --radius: 8px;
  --max-w: 1180px;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
           "Microsoft YaHei", "Noto Sans SC", Roboto, Helvetica, Arial,
           sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 76px; }

body {
  margin: 0;
  font-family: var(--sans);
  color: var(--ink);
  background: var(--paper);
  line-height: 1.6;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 { font-weight: 700; line-height: 1.3; letter-spacing: -0.01em; }
h1 { font-size: 2rem; margin: 0 0 0.4em; }
h2 { font-size: 1.5rem; margin: 0 0 0.6em; padding-top: 0.2em; border-top: 2px solid var(--ink); padding-top: 12px; }
h3 { font-size: 1.15rem; margin: 1.6em 0 0.5em; }
p { margin: 0 0 1em; color: var(--ink-soft); }
a { color: var(--accent); }
code, .mono { font-family: var(--mono); font-size: 0.92em; }

.lang-en { color: var(--ink-faint); font-weight: 500; font-size: 0.82em; display: block; }
.zh { display: block; }

.container { max-width: var(--max-w); margin: 0 auto; padding: 0 24px; }

/* ---------- Sticky nav ---------- */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.96);
  border-bottom: 1px solid var(--line);
  backdrop-filter: saturate(140%) blur(6px);
}
.site-nav .container { display: flex; align-items: center; gap: 20px; padding: 10px 24px; }
.brand { font-weight: 800; font-size: 1rem; white-space: nowrap; color: var(--ink); text-decoration: none; }
.brand .tag { color: var(--accent); }
.nav-links {
  display: flex; gap: 2px; overflow-x: auto; scrollbar-width: none;
  flex: 1;
}
.nav-links::-webkit-scrollbar { display: none; }
.nav-links a {
  white-space: nowrap; text-decoration: none; color: var(--ink-soft);
  font-size: 0.86rem; font-weight: 600; padding: 8px 10px; border-radius: 6px;
}
.nav-links a:hover { background: var(--paper-sunk); color: var(--ink); }
.nav-actions { display: flex; gap: 8px; flex-shrink: 0; }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex; align-items: center; gap: 6px;
  font-family: var(--sans); font-size: 0.85rem; font-weight: 600;
  min-height: 40px; padding: 8px 14px; border-radius: 6px; border: 1px solid var(--line);
  background: var(--paper); color: var(--ink); cursor: pointer;
  text-decoration: none; transition: background .12s, border-color .12s;
}
.btn:hover { background: var(--paper-sunk); border-color: var(--ink-faint); }
.btn-accent { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn-accent:hover { background: #094e4a; border-color: #094e4a; }
.btn-sm { padding: 5px 10px; font-size: 0.78rem; }
.btn[data-copied="true"] { background: var(--accent-soft); border-color: var(--accent); color: var(--accent); }

/* ---------- Hero ---------- */
.hero { padding: 56px 0 40px; border-bottom: 1px solid var(--line); background: var(--paper-sunk); }
.hero .kicker {
  display: inline-block; font-size: 0.75rem; font-weight: 700; letter-spacing: 0.06em;
  text-transform: uppercase; color: var(--accent); background: var(--accent-soft);
  padding: 4px 10px; border-radius: 999px; margin-bottom: 14px;
}
.hero h1 { max-width: 820px; }
.hero .sub { max-width: 720px; font-size: 1.05rem; }
.hero .meta { display: flex; flex-wrap: wrap; gap: 8px 20px; font-size: 0.82rem; color: var(--ink-faint); margin-top: 18px; }
.hero .meta b { color: var(--ink-soft); }

/* ---------- Sections ---------- */
section.block { padding: 44px 0; border-bottom: 1px solid var(--line-soft); }
section.block:last-of-type { border-bottom: none; }
.section-head { max-width: 780px; margin-bottom: 24px; }
.section-num { font-family: var(--mono); color: var(--ink-faint); font-size: 0.85rem; }

/* ---------- Priority badges ---------- */
.badge { display: inline-block; font-family: var(--mono); font-size: 0.72rem; font-weight: 700;
  padding: 2px 7px; border-radius: 4px; letter-spacing: 0.02em; }
.badge-P0 { background: var(--p0-bg); color: var(--p0); }
.badge-P1 { background: var(--p1-bg); color: var(--p1); }
.badge-P2 { background: var(--p2-bg); color: var(--p2); }

/* ---------- Cards / grid ---------- */
.grid { display: grid; gap: 16px; }
.grid-3 { grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); }
.grid-2 { grid-template-columns: repeat(auto-fit, minmax(320px, 1fr)); }
.card {
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--paper-card);
  padding: 18px 20px;
}
.card h4 { margin: 0 0 8px; font-size: 1rem; display: flex; justify-content: space-between; align-items: center; gap: 8px; }
.card p:last-child { margin-bottom: 0; }
.card ul { margin: 0.4em 0 0; padding-left: 1.2em; color: var(--ink-soft); }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; border: 1px solid var(--line); border-radius: var(--radius); }
table { border-collapse: collapse; width: 100%; font-size: 0.86rem; }
thead th {
  position: sticky; top: 0; background: var(--ink); color: #fff; text-align: left;
  font-weight: 600; padding: 9px 12px; white-space: nowrap;
}
tbody td { padding: 8px 12px; border-top: 1px solid var(--line-soft); vertical-align: top; }
tbody tr:nth-child(even) { background: var(--paper-sunk); }
td.mono, th.mono { font-family: var(--mono); font-size: 0.82rem; }
.leg-cell { background: var(--accent-soft); font-weight: 700; }
.strike-cell { background: var(--paper-sunk); font-weight: 700; }
.small-note { font-size: 0.8rem; color: var(--ink-faint); margin-top: 8px; }

/* ---------- Data product tabs ---------- */
.tabs { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 14px; }
.tab-btn {
  min-height: 40px; font-family: var(--sans); font-size: 0.82rem; font-weight: 600; padding: 7px 12px;
  border-radius: 999px; border: 1px solid var(--line); background: var(--paper); cursor: pointer; color: var(--ink-soft);
}
.tab-btn[aria-selected="true"] { background: var(--ink); color: #fff; border-color: var(--ink); }
.tab-panel { display: none; }
.tab-panel[data-active="true"] { display: block; }

/* ---------- Downloads ---------- */
.download-list { list-style: none; margin: 0; padding: 0; display: grid; gap: 10px; }
.download-list li {
  display: flex; justify-content: space-between; align-items: center; gap: 12px;
  border: 1px solid var(--line); border-radius: var(--radius); padding: 12px 16px; background: var(--paper-card);
}
.download-list .fname { font-family: var(--mono); font-weight: 700; font-size: 0.88rem; }
.download-list .fdesc { color: var(--ink-faint); font-size: 0.8rem; display: block; margin-top: 2px; }

/* ---------- Chart panels ---------- */
.chart-panel {
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--paper-card);
  padding: 16px 18px 20px;
}
.chart-panel h4 { margin: 0 0 4px; }
.chart-panel .chart-note { font-size: 0.8rem; color: var(--ink-faint); margin-bottom: 12px; }
.chart-panel svg { width: 100%; height: auto; display: block; }
.legend { display: flex; flex-wrap: wrap; gap: 14px; font-size: 0.78rem; color: var(--ink-soft); margin-top: 10px; }
.legend .sw { display: inline-block; width: 10px; height: 10px; border-radius: 2px; margin-right: 5px; vertical-align: -1px; }

.disclaimer-strip {
  background: var(--p1-bg); border: 1px solid #e9dca0; color: #6b5600;
  border-radius: var(--radius); padding: 10px 14px; font-size: 0.82rem; margin: 16px 0;
}

/* ---------- Checklist ---------- */
.checklist { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.checklist li {
  padding: 10px 14px 10px 38px; position: relative; border: 1px solid var(--line);
  border-radius: 6px; background: var(--paper-card); font-size: 0.92rem;
}
.checklist li::before {
  content: ""; position: absolute; left: 14px; top: 13px; width: 12px; height: 12px;
  border: 2px solid var(--accent); border-radius: 3px;
}

/* ---------- Footer ---------- */
footer { border-top: 1px solid var(--line); padding: 28px 0 40px; color: var(--ink-faint); font-size: 0.82rem; }
footer .container { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 10px; }

/* ---------- Responsive ---------- */
@media (max-width: 720px) {
  h1 { font-size: 1.5rem; }
  h2 { font-size: 1.25rem; }
  html { scroll-padding-top: 118px; }
  .site-nav .container { flex-wrap: wrap; gap: 8px 12px; padding: 8px 16px; }
  .brand { min-width: 0; }
  .nav-actions { margin-left: auto; gap: 6px; }
  .nav-actions .btn { min-height: 36px; padding: 6px 9px; font-size: 0.78rem; }
  .nav-links { order: 3; flex: 1 0 100%; width: 100%; }
  .nav-actions .btn span.full { display: none; }
  .hero { padding: 36px 0 28px; }
  section.block { padding: 30px 0; }
  .container { padding: 0 16px; }
}

@media (max-width: 420px) {
  .brand .tag { display: none; }
  .download-list li { align-items: flex-start; flex-direction: column; }
  .download-list .btn { align-self: stretch; justify-content: center; }
}

/* ---------- Print ---------- */
@media print {
  .site-nav, .nav-actions, .btn, .tabs { display: none !important; }
  body { font-size: 12px; }
  a { color: inherit; text-decoration: underline; }
  section.block { border-bottom: none; page-break-inside: avoid; padding: 14px 0; }
  .chart-panel, .card, table { page-break-inside: avoid; }
  .hero { background: none; border-bottom: 1px solid #000; }
  .tab-panel { display: block !important; }
}