:root {
  --ink: #1a2332;
  --muted: #5b6778;
  --line: #d5dbe6;
  --soft: #ffffff;
  --paper: #eef1f6;
  --brand: #0b6efd;
  --brand-deep: #084db3;
  --rail: #e3e8f0;
  --rail-ink: #243044;
  --max: 1180px;
  --radius: 8px;
  font-family: "Source Han Sans SC", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
}

*,
*::before,
*::after { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  color: var(--ink);
  background: linear-gradient(180deg, #f5f7fb 0%, var(--paper) 50%, #e8edf5 100%);
  line-height: 1.75;
  min-height: 100vh;
}

a { color: var(--brand-deep); text-underline-offset: 3px; }
a:hover { color: var(--brand); }
img { max-width: 100%; height: auto; display: block; }
.wrap { width: min(100% - 2rem, var(--max)); margin-inline: auto; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 40;
  background: rgba(238, 241, 246, 0.96);
  border-bottom: 1px solid var(--line);
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.65rem 0;
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
}
.brand img { width: 36px; height: 36px; border-radius: 8px; object-fit: cover; }
.nav-desktop { display: flex; gap: 1rem; flex-wrap: wrap; }
.nav-desktop a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.92rem;
}
.nav-desktop a:hover { color: var(--brand); }
.menu-toggle {
  display: none;
  border: 1px solid var(--brand);
  background: #fff;
  color: var(--brand-deep);
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius);
  cursor: pointer;
}
#mobile-nav {
  display: none;
  flex-direction: column;
  gap: 0.35rem;
  padding: 0 1rem 0.85rem;
  border-top: 1px solid var(--line);
}
#mobile-nav.open { display: flex; }
#mobile-nav a {
  color: var(--ink);
  text-decoration: none;
  padding: 0.45rem 0;
}

.ads-slot { margin-bottom: 0.15rem; }

/* rail-first layout */
.rail-shell {
  display: grid;
  grid-template-columns: 220px minmax(0, 1fr);
  gap: 0;
  margin: 0.75rem auto 2rem;
  width: min(100% - 2rem, var(--max));
  border: 1px solid var(--line);
  background: #fff;
  min-height: 70vh;
}

.rail-nav {
  background: var(--rail);
  border-right: 1px solid var(--line);
  padding: 1.1rem 0.85rem;
  position: sticky;
  top: 58px;
  align-self: start;
  max-height: calc(100vh - 70px);
  overflow: auto;
}
.rail-nav .rail-title {
  margin: 0 0 0.75rem;
  font-size: 0.78rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  font-weight: 700;
}
.rail-nav a {
  display: block;
  text-decoration: none;
  color: var(--rail-ink);
  padding: 0.55rem 0.65rem;
  margin-bottom: 0.3rem;
  border-left: 3px solid transparent;
  background: rgba(255, 255, 255, 0.55);
  border-radius: 0 6px 6px 0;
  font-size: 0.92rem;
  font-weight: 600;
}
.rail-nav a:hover,
.rail-nav a:focus {
  border-left-color: var(--brand);
  background: #fff;
  color: var(--brand-deep);
}
.rail-hint {
  margin-top: 1rem;
  padding: 0.7rem;
  font-size: 0.82rem;
  color: var(--muted);
  background: rgba(11, 110, 253, 0.08);
  border-radius: 6px;
}

.rail-main {
  padding: 1.25rem 1.4rem 2rem;
}
.rail-main h1 {
  margin: 0 0 0.55rem;
  font-size: clamp(1.45rem, 2.8vw, 2rem);
  line-height: 1.35;
}
.lead {
  margin: 0 0 1.1rem;
  color: var(--muted);
  font-size: 1.02rem;
}
.rail-main h2 {
  margin: 1.55rem 0 0.65rem;
  font-size: 1.28rem;
  color: var(--ink);
  border-bottom: 2px solid var(--brand);
  padding-bottom: 0.3rem;
  display: inline-block;
  min-width: 40%;
}
.rail-main h3 {
  margin: 1.1rem 0 0.45rem;
  font-size: 1.05rem;
  color: var(--brand-deep);
}
.rail-main p { margin: 0 0 0.85rem; }
.rail-main ul { margin: 0 0 1rem; padding-left: 1.2rem; }
.rail-main li { margin-bottom: 0.35rem; }

.rail-hero-fig {
  margin: 0 0 1.1rem;
  border: 1px solid var(--line);
  background: var(--paper);
}
.rail-hero-fig img {
  width: 100%;
  aspect-ratio: 16/9;
  object-fit: cover;
}
.rail-hero-fig figcaption,
.rail-grid figcaption {
  padding: 0.5rem 0.75rem;
  font-size: 0.88rem;
  color: var(--muted);
}

.rail-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.9rem;
  margin: 1rem 0;
}
.rail-grid figure {
  margin: 0;
  border: 1px solid var(--line);
  background: var(--paper);
}
.rail-grid img {
  width: 100%;
  aspect-ratio: 4/3;
  object-fit: cover;
}

.util-strip {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin: 1rem 0;
  padding: 0.75rem;
  background: var(--rail);
  border: 1px solid var(--line);
}
.util-strip a {
  text-decoration: none;
  background: #fff;
  border: 1px solid var(--brand);
  color: var(--brand-deep);
  padding: 0.3rem 0.65rem;
  border-radius: 4px;
  font-size: 0.86rem;
  font-weight: 600;
}

.peer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  align-items: center;
  margin: 1.1rem 0;
  padding: 0.8rem 1rem;
  border: 1px solid var(--line);
  background: #f8faff;
}
.peer-links a { font-weight: 600; }

.faq details {
  border: 1px solid var(--line);
  background: #fafbfd;
  padding: 0.7rem 0.9rem;
  margin-bottom: 0.5rem;
}
.faq summary { cursor: pointer; font-weight: 600; }
.faq p { margin: 0.5rem 0 0; }

.page-hero { padding: 1.4rem 0 0.4rem; }
.page-hero h1 { margin: 0 0 0.35rem; font-size: 1.65rem; }
.muted { color: var(--muted); }
.prose { padding-bottom: 2rem; max-width: 48rem; }
.prose h2 { margin-top: 1.35rem; font-size: 1.15rem; color: var(--brand-deep); }

.err-box { padding: 3rem 0; text-align: center; }
.btn {
  display: inline-block;
  padding: 0.55rem 1.1rem;
  border-radius: var(--radius);
  text-decoration: none;
  border: 1px solid var(--brand);
}
.btn-primary { background: var(--brand); color: #fff; }
.btn-primary:hover { background: var(--brand-deep); color: #fff; }

.site-footer {
  border-top: 1px solid var(--line);
  background: #e4e9f2;
  padding: 1.2rem 0 1.5rem;
  font-size: 0.92rem;
  color: var(--muted);
}
.footer-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem;
  margin-bottom: 0.5rem;
}
.footer-nav a { color: var(--brand-deep); text-decoration: none; }

@media (max-width: 900px) {
  .rail-shell { grid-template-columns: 1fr; }
  .rail-nav {
    position: static;
    max-height: none;
    border-right: 0;
    border-bottom: 1px solid var(--line);
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.35rem;
  }
  .rail-nav .rail-title,
  .rail-hint { grid-column: 1 / -1; }
  .rail-grid { grid-template-columns: 1fr; }
  .nav-desktop { display: none; }
  .menu-toggle { display: inline-block; }
}

/* SEO keyword highlight */
strong.kw, .kw{color:var(--accent,var(--brand,#c43b2c));font-weight:700}
mark.kw{background:rgba(196,59,44,.12);color:inherit;padding:0 .15em;border-radius:3px}