:root {
  --bg: #f6f7f9;
  --card: #ffffff;
  --line: #e3e6eb;
  --ink: #1b2430;
  --ink-2: #4a5566;
  --ink-3: #78828f;
  --brand: #1f5fd0;
  --brand-dark: #17479c;
  --brand-soft: #eef3fd;
  --radius: 10px;
  --wrap: 1080px;
}

* {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: system-ui, -apple-system, "Segoe UI", "PingFang SC", "Hiragino Sans GB",
    "Microsoft YaHei", "Noto Sans SC", sans-serif;
  font-size: 16px;
  line-height: 1.75;
}

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

a:hover {
  color: var(--brand-dark);
  text-decoration: underline;
}

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

.skip {
  position: absolute;
  left: -9999px;
}

/* ---------- header ---------- */

.site-header {
  background: var(--card);
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 20;
}

.header-inner {
  display: flex;
  align-items: center;
  gap: 20px;
  min-height: 60px;
  flex-wrap: wrap;
  padding-top: 8px;
  padding-bottom: 8px;
}

.logo {
  font-weight: 700;
  font-size: 1.06rem;
  color: var(--ink);
  display: inline-flex;
  align-items: center;
  gap: 7px;
  white-space: nowrap;
}

.logo:hover {
  text-decoration: none;
  color: var(--brand);
}

.logo-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 24px;
  height: 24px;
  border-radius: 6px;
  background: var(--brand);
  color: #fff;
  font-size: 0.82rem;
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 2px 16px;
  font-size: 0.9rem;
}

.site-nav a {
  color: var(--ink-2);
}

/* ---------- main ---------- */

main {
  padding: 28px 20px 56px;
}

h1 {
  font-size: clamp(1.45rem, 4.2vw, 1.95rem);
  line-height: 1.4;
  margin: 0 0 14px;
  letter-spacing: -0.01em;
}

h2 {
  font-size: 1.14rem;
  margin: 34px 0 10px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--line);
}

h3 {
  font-size: 1rem;
  margin: 18px 0 8px;
}

p {
  margin: 0 0 12px;
  color: var(--ink-2);
}

.lead {
  font-size: 1.02rem;
  color: var(--ink-2);
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 18px;
  margin: 0 0 8px;
}

.note {
  font-size: 0.88rem;
  color: var(--ink-3);
}

.breadcrumb {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  padding: 0;
  margin: 0 0 14px;
  font-size: 0.83rem;
  color: var(--ink-3);
}

.breadcrumb li + li::before {
  content: "/";
  margin: 0 7px 0 3px;
  color: #c3c9d2;
}

/* ---------- answer ---------- */

.answer {
  background: linear-gradient(180deg, #fff, #fbfcfe);
  border: 1px solid #d7e2f7;
  border-left: 4px solid var(--brand);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin: 0 0 18px;
}

.answer-main {
  font-size: 1.22rem;
  color: var(--ink);
  margin: 0 0 6px;
}

.answer-main strong {
  color: var(--brand-dark);
  font-size: 1.32rem;
}

.answer-sub {
  margin: 0;
  font-size: 0.94rem;
  color: var(--ink-2);
}

.formula {
  font-family: ui-monospace, "SF Mono", Consolas, "Liberation Mono", monospace;
  background: #f2f4f8;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px 14px;
  font-size: 0.98rem;
  color: var(--ink);
  overflow-x: auto;
}

/* ---------- converter ---------- */

.converter {
  display: grid;
  grid-template-columns: 1.1fr 1.2fr 1.2fr;
  gap: 12px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px;
  margin: 0 0 4px;
}

.conv-field {
  display: flex;
  flex-direction: column;
  gap: 5px;
}

.conv-field label {
  font-size: 0.8rem;
  color: var(--ink-3);
}

.converter input,
.converter select {
  width: 100%;
  padding: 9px 10px;
  font-size: 0.98rem;
  font-family: inherit;
  color: var(--ink);
  border: 1px solid #ccd3dd;
  border-radius: 7px;
  background: #fff;
}

.converter input:focus,
.converter select:focus {
  outline: 2px solid #b9cdf2;
  border-color: var(--brand);
}

.conv-result {
  grid-column: 1 / -1;
  background: var(--brand-soft);
  border-radius: 8px;
  padding: 10px 14px;
  font-size: 1rem;
  color: var(--brand-dark);
  font-weight: 600;
  word-break: break-all;
}

/* ---------- tables ---------- */

.table-scroll {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--card);
}

table.conv-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.94rem;
}

.conv-table caption {
  caption-side: top;
  text-align: left;
  padding: 11px 14px;
  font-size: 0.84rem;
  color: var(--ink-3);
  border-bottom: 1px solid var(--line);
}

.conv-table th {
  background: #f4f6fa;
  text-align: left;
  font-weight: 600;
  font-size: 0.86rem;
  color: var(--ink-2);
  padding: 9px 14px;
  white-space: nowrap;
  border-bottom: 1px solid var(--line);
}

.conv-table td {
  padding: 9px 14px;
  border-bottom: 1px solid #f0f2f6;
  color: var(--ink-2);
}

.conv-table tr:last-child td {
  border-bottom: 0;
}

.conv-table tbody tr:nth-child(even) {
  background: #fbfcfe;
}

.conv-table td.num,
.conv-table td.sym {
  font-variant-numeric: tabular-nums;
  color: var(--ink);
  white-space: nowrap;
}

.mini-link {
  font-size: 0.84rem;
}

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

.cat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 12px;
  margin: 14px 0 0;
}

.cat-card {
  display: flex;
  flex-direction: column;
  gap: 4px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px 16px;
  color: inherit;
  transition: border-color 0.15s, transform 0.15s;
}

.cat-card:hover {
  border-color: #b9cdf2;
  transform: translateY(-1px);
  text-decoration: none;
}

.cat-name {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--ink);
}

.cat-meta {
  font-size: 0.8rem;
  color: var(--brand);
  background: var(--brand-soft);
  border-radius: 20px;
  padding: 2px 9px;
  align-self: flex-start;
}

.cat-desc {
  font-size: 0.86rem;
  color: var(--ink-3);
  line-height: 1.6;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.feat-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 12px 0 0;
}

.feat-link {
  font-size: 0.9rem;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 20px;
  padding: 5px 14px;
  color: var(--ink-2);
}

.feat-link:hover {
  border-color: #b9cdf2;
  color: var(--brand);
  text-decoration: none;
}

.about-block p {
  max-width: 74ch;
}

/* ---------- category ---------- */

.unit-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  gap: 10px;
  margin: 14px 0 0;
}

.unit-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  display: flex;
  flex-direction: column;
  color: inherit;
}

.unit-card:hover {
  border-color: #b9cdf2;
  text-decoration: none;
}

.unit-name {
  font-weight: 600;
  color: var(--ink);
}

.unit-symbol {
  font-size: 0.82rem;
  color: var(--ink-3);
}

.all-pairs > summary {
  cursor: pointer;
  padding: 10px 14px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  font-size: 0.92rem;
  color: var(--brand);
  font-weight: 600;
  margin-bottom: 12px;
  list-style: none;
}

.all-pairs > summary::-webkit-details-marker {
  display: none;
}

.all-pairs > summary::before {
  content: "＋";
  margin-right: 8px;
  color: var(--ink-3);
}

.all-pairs[open] > summary::before {
  content: "－";
}

.all-pairs[open] > summary {
  margin-bottom: 12px;
}

.group {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 4px 16px 12px;
  margin: 0 0 10px;
}

.group h3 {
  margin: 12px 0 8px;
  font-size: 0.95rem;
}

.group-links,
.rel-links {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 14px;
  font-size: 0.9rem;
}

.cat-note {
  background: var(--card);
  border: 1px solid var(--line);
  border-left: 3px solid #c9d6ee;
  border-radius: var(--radius);
  padding: 4px 18px 8px;
}

.cat-note h2 {
  margin-top: 12px;
  font-size: 1.02rem;
}

/* ---------- pair page ---------- */

.def-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 12px;
}

.def {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 4px 16px 10px;
}

.def h3 {
  font-size: 0.98rem;
  color: var(--ink);
}

.def p {
  font-size: 0.9rem;
  margin: 0 0 10px;
}

.rel-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 16px;
}

.rel-col h3 {
  font-size: 0.92rem;
  color: var(--ink-3);
  font-weight: 600;
  margin: 0 0 8px;
}

.faq dl {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 6px 18px;
  margin: 0;
}

.faq dt {
  font-weight: 600;
  color: var(--ink);
  margin: 14px 0 4px;
}

.faq dd {
  margin: 0 0 12px;
  color: var(--ink-2);
  font-size: 0.94rem;
}

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

.site-footer {
  background: var(--card);
  border-top: 1px solid var(--line);
  padding: 28px 0 34px;
  font-size: 0.86rem;
  color: var(--ink-3);
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 18px;
  margin-bottom: 12px;
}

.footer-note {
  max-width: 78ch;
  font-size: 0.82rem;
  line-height: 1.7;
  color: var(--ink-3);
}

.copyright {
  margin: 10px 0 0;
  font-size: 0.8rem;
  color: #9aa3ae;
}

.beian {
  margin: 4px 0 0;
  font-size: 0.8rem;
  display: flex;
  flex-wrap: wrap;
  gap: 4px 14px;
}

.beian a {
  color: #78828f;
}

.beian a:hover {
  color: var(--brand);
}

.notfound {
  text-align: center;
  padding: 40px 0;
}

.btn {
  display: inline-block;
  background: var(--brand);
  color: #fff;
  padding: 9px 20px;
  border-radius: 7px;
  margin: 6px 0 18px;
}

.btn:hover {
  background: var(--brand-dark);
  color: #fff;
  text-decoration: none;
}

/* ---------- responsive ---------- */

@media (max-width: 720px) {
  body {
    font-size: 15.5px;
  }

  .header-inner {
    gap: 10px;
  }

  .site-nav {
    gap: 2px 12px;
    font-size: 0.84rem;
    max-height: 62px;
    overflow-y: auto;
  }

  .converter {
    grid-template-columns: 1fr 1fr;
  }

  .converter .conv-field:first-child {
    grid-column: 1 / -1;
  }

  .answer-main {
    font-size: 1.08rem;
  }

  main {
    padding-top: 20px;
  }

  .cat-grid {
    grid-template-columns: 1fr 1fr;
  }

  .cat-desc {
    display: none;
  }
}

@media (max-width: 420px) {
  .cat-grid {
    grid-template-columns: 1fr;
  }
}