/* Startup Due Diligence - site stylesheet
   Editorial research archive. Light/dark via prefers-color-scheme.
   Display: Source Serif 4 (self-hosted, latin) with CJK serif fallbacks.
   Body: system sans stack. */

@font-face {
  font-family: "Source Serif 4";
  font-style: normal;
  font-weight: 600;
  font-display: swap;
  src: url("fonts/source-serif-4-latin-600.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+2013-2014, U+2018-201D, U+2026;
}
@font-face {
  font-family: "Source Serif 4";
  font-style: italic;
  font-weight: 400;
  font-display: swap;
  src: url("fonts/source-serif-4-latin-400-italic.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+2013-2014, U+2018-201D, U+2026;
}

:root {
  --bg: #fbfbfa;
  --surface: #f4f4f1;
  --ink: #20242a;
  --ink-2: #565e66;
  --faint: #6e757c;
  --line: #e6e7e3;
  --line-strong: #c8cbc6;
  --accent: #156b4e;
  --accent-soft: rgba(21, 107, 78, 0.35);
  --serif: "Source Serif 4", Georgia, "Songti SC", "Noto Serif CJK SC", "SimSun", serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --mono: ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #141615;
    --surface: #1b1e1c;
    --ink: #e7e9e7;
    --ink-2: #a9b0ab;
    --faint: #868d88;
    --line: #292d2b;
    --line-strong: #3e4340;
    --accent: #55c08f;
    --accent-soft: rgba(85, 192, 143, 0.4);
  }
}

* { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.7;
}
html[lang="zh-CN"] body { line-height: 1.85; }

.wrap {
  max-width: 1120px;
  margin-inline: auto;
  padding-inline: clamp(20px, 4vw, 40px);
}

a { color: var(--accent); text-decoration: none; }

/* ---------- top navigation ---------- */

.nav {
  border-bottom: 1px solid var(--line);
}
.nav-inner {
  display: flex;
  align-items: center;
  gap: 28px;
  height: 64px;
}
.wordmark {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
  color: var(--ink);
  margin-right: auto;
  white-space: nowrap;
}
.nav-links {
  display: flex;
  align-items: center;
  gap: 22px;
  font-size: 0.9rem;
}
.nav-links a { color: var(--ink-2); transition: color 0.15s ease; }
.nav-links a:hover { color: var(--ink); }
.lang {
  display: flex;
  gap: 10px;
  font-size: 0.85rem;
  padding-left: 22px;
  border-left: 1px solid var(--line);
}
.lang a { color: var(--faint); transition: color 0.15s ease; }
.lang a:hover { color: var(--ink); }
.lang .on { color: var(--ink); font-weight: 600; }

@media (max-width: 640px) {
  .nav-inner { gap: 16px; }
  .nav-links { gap: 14px; }
  .nav-links .hide-sm { display: none; }
  .lang { padding-left: 14px; }
}

/* ---------- home masthead ---------- */

.hero { padding: clamp(56px, 9vh, 96px) 0 clamp(40px, 6vh, 64px); }
.hero h1 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: clamp(2.3rem, 5.5vw, 3.4rem);
  line-height: 1.12;
  letter-spacing: -0.02em;
  margin: 0 0 20px;
  max-width: 22ch;
}
.hero p {
  font-size: 1.08rem;
  color: var(--ink-2);
  max-width: 52ch;
  margin: 0 0 18px;
}
.hero-meta {
  font-family: var(--mono);
  font-size: 0.78rem;
  color: var(--faint);
}

/* ---------- company directory ---------- */

.directory { padding-bottom: 40px; }
.directory h2 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.35rem;
  letter-spacing: -0.01em;
  margin: 0 0 14px;
}
.dir { border-bottom: 1px solid var(--line); }
.dir-row {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr) auto;
  gap: 8px 28px;
  align-items: baseline;
  padding: 17px 8px;
  margin: 0 -8px;
  border-top: 1px solid var(--line);
  border-radius: 6px;
  transition: background 0.15s ease;
}
.dir-row:hover { background: var(--surface); }
.dir-name {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.2rem;
  letter-spacing: -0.01em;
  color: var(--ink);
  transition: color 0.15s ease;
}
.dir-row:hover .dir-name { color: var(--accent); }
.dir-area { font-size: 0.92rem; color: var(--ink-2); }
.dir-date {
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--faint);
  white-space: nowrap;
}
@media (max-width: 720px) {
  .dir-row { grid-template-columns: minmax(0, 1fr) auto; gap: 2px 16px; }
  .dir-area { grid-column: 1 / -1; }
}

/* ---------- article / prose ---------- */

.doc {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 48px;
  padding: clamp(36px, 6vh, 64px) 0 48px;
}
@media (min-width: 1100px) {
  .doc.has-toc {
    grid-template-columns: minmax(0, 730px) 210px;
    justify-content: space-between;
  }
}

.prose { max-width: 730px; min-width: 0; }

.doc-head { margin-bottom: 8px; }
.doc-head h1 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: clamp(1.9rem, 4vw, 2.5rem);
  line-height: 1.15;
  letter-spacing: -0.02em;
  margin: 0 0 10px;
}
.doc-meta {
  font-size: 0.88rem;
  color: var(--ink-2);
  margin: 0 0 6px;
}
.doc-meta .date {
  font-family: var(--mono);
  font-size: 0.75rem;
  color: var(--faint);
}

.prose h1 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 2.1rem;
  line-height: 1.15;
  letter-spacing: -0.02em;
  margin: 0 0 16px;
}
.prose h2 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.45rem;
  line-height: 1.25;
  letter-spacing: -0.015em;
  margin: 44px 0 14px;
  scroll-margin-top: 28px;
}
.prose h3 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 1.12rem;
  margin: 32px 0 10px;
  scroll-margin-top: 28px;
}
.prose p, .prose ul, .prose ol { margin: 0 0 16px; }
.prose li { margin-bottom: 6px; }
.prose ul, .prose ol { padding-left: 1.35em; }
.prose a {
  text-decoration: underline;
  text-decoration-color: var(--accent-soft);
  text-underline-offset: 2.5px;
  text-decoration-thickness: 1px;
  transition: text-decoration-color 0.15s ease;
}
.prose a:hover { text-decoration-color: var(--accent); }
.prose strong { font-weight: 650; }
.prose hr {
  border: 0;
  border-top: 1px solid var(--line);
  margin: 44px 0;
}
.prose blockquote {
  margin: 0 0 20px;
  padding: 2px 0 2px 16px;
  border-left: 2px solid var(--line-strong);
  color: var(--ink-2);
  font-size: 0.92rem;
}
.prose blockquote p { margin-bottom: 4px; }
.prose code {
  font-family: var(--mono);
  font-size: 0.84em;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 0.08em 0.35em;
}
.prose pre {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 14px 16px;
  overflow-x: auto;
  margin: 0 0 20px;
}
.prose pre code { background: none; border: 0; padding: 0; font-size: 0.82rem; }

/* tables: research pages are table-heavy; wide ones scroll inside their wrapper */
.table-wrap { overflow-x: auto; margin: 0 0 22px; }
.prose table {
  border-collapse: collapse;
  width: 100%;
  font-size: 0.86rem;
  line-height: 1.55;
}
.prose th {
  text-align: left;
  font-weight: 600;
  font-size: 0.8rem;
  color: var(--ink-2);
  padding: 8px 14px 8px 0;
  border-bottom: 1px solid var(--line-strong);
  white-space: nowrap;
}
.prose td {
  vertical-align: top;
  padding: 9px 14px 9px 0;
  border-top: 1px solid var(--line);
  min-width: 7em;
}
.prose tr:first-child td { border-top: 0; }
.prose th:last-child, .prose td:last-child { padding-right: 0; }

/* ---------- table of contents rail ---------- */

.toc { display: none; }
@media (min-width: 1100px) {
  .doc.has-toc .toc {
    display: block;
    position: sticky;
    top: 36px;
    align-self: start;
    max-height: calc(100vh - 72px);
    overflow-y: auto;
    font-size: 0.8rem;
    padding-left: 18px;
    border-left: 1px solid var(--line);
  }
}
.toc-title {
  font-weight: 600;
  font-size: 0.78rem;
  color: var(--ink);
  margin: 0 0 10px;
}
.toc ol { list-style: none; margin: 0; padding: 0; }
.toc li { margin: 0 0 8px; }
.toc a {
  color: var(--faint);
  display: block;
  line-height: 1.45;
  transition: color 0.15s ease;
}
.toc a:hover { color: var(--ink); }
.toc a.active { color: var(--accent); }

/* ---------- footer ---------- */

.footer {
  border-top: 1px solid var(--line);
  margin-top: 32px;
  padding: 28px 0 44px;
  font-size: 0.82rem;
  color: var(--faint);
}
.footer p { margin: 0 0 6px; max-width: 72ch; }
.footer a { color: var(--ink-2); text-decoration: underline; text-decoration-color: var(--line-strong); text-underline-offset: 2px; }
.footer a:hover { color: var(--ink); }