:root {
  --ink: #0f172a;
  --muted: #55627a;
  --accent: #4f46e5;
  --accent-dark: #3730a3;
  --accent-soft: #eef2ff;
  --line: #e2e8f0;
  --bg: #f8fafc;
  --card: #ffffff;
  --ok: #047857;
  --warn: #b45309;
  --radius: 14px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

.wrap { max-width: 980px; margin: 0 auto; padding: 0 20px; }

/* ---------- diagrams ---------- */
.diagram {
  margin: 18px 0;
  padding: 14px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}
.diagram svg { display: block; width: 100%; height: auto; }
.diagram figcaption {
  margin-top: 8px;
  font-size: 0.85rem;
  color: var(--muted);
  text-align: center;
}

/* ---------- header / footer ---------- */
.site-header {
  background: var(--card);
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 20;
}
.site-header .wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding-top: 12px;
  padding-bottom: 12px;
  flex-wrap: wrap;
}
.brand {
  font-weight: 800;
  font-size: 1.15rem;
  color: var(--ink);
  text-decoration: none;
  letter-spacing: -0.02em;
}
.brand span { color: var(--accent); }
.top-nav { display: flex; gap: 4px; flex-wrap: wrap; }
.top-nav a {
  text-decoration: none;
  color: var(--muted);
  font-size: 0.88rem;
  padding: 6px 10px;
  border-radius: 8px;
}
.top-nav a:hover { background: var(--accent-soft); color: var(--accent-dark); }

.site-footer {
  border-top: 1px solid var(--line);
  background: var(--card);
  margin-top: 56px;
  padding: 28px 0 40px;
  color: var(--muted);
  font-size: 0.88rem;
}
.site-footer a { color: var(--muted); }
.footer-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 24px;
}
.footer-grid h4 { margin: 0 0 8px; color: var(--ink); font-size: 0.92rem; }
.footer-grid ul { margin: 0; padding: 0; list-style: none; }
.footer-grid li { margin: 4px 0; }

/* ---------- breadcrumb ---------- */
.crumbs {
  font-size: 0.82rem;
  color: var(--muted);
  padding: 14px 0 0;
}
.crumbs a { color: var(--muted); text-decoration: none; }
.crumbs a:hover { color: var(--accent); }

/* ---------- hero ---------- */
.hero { padding: 34px 0 10px; }
.hero h1 {
  font-size: clamp(1.6rem, 4vw, 2.3rem);
  line-height: 1.2;
  letter-spacing: -0.02em;
  margin: 0 0 12px;
}
.hero p.lede { color: var(--muted); font-size: 1.05rem; max-width: 760px; margin: 0 0 8px; }

/* ---------- calculator card ---------- */
.calc-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 22px;
  margin: 22px 0;
  box-shadow: 0 1px 2px rgba(15, 23, 42, 0.04);
}
.calc-card h2 { margin: 0 0 4px; font-size: 1.25rem; }
.calc-card .sub { color: var(--muted); font-size: 0.92rem; margin: 0 0 16px; }

.fields {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(170px, 1fr));
  gap: 14px;
}
.field label {
  display: block;
  font-size: 0.82rem;
  font-weight: 600;
  margin-bottom: 4px;
  color: var(--ink);
}
.field .hint { font-weight: 400; color: var(--muted); }
.field input, .field select {
  width: 100%;
  padding: 10px 10px;
  border: 1px solid #cbd5e1;
  border-radius: 9px;
  font-size: 0.95rem;
  background: #fff;
  color: var(--ink);
}
.field input:focus, .field select:focus {
  outline: 2px solid var(--accent);
  outline-offset: 1px;
  border-color: var(--accent);
}
.unit-toggle {
  display: inline-flex;
  border: 1px solid #cbd5e1;
  border-radius: 9px;
  overflow: hidden;
  margin-bottom: 14px;
}
.unit-toggle button {
  border: 0;
  background: #fff;
  padding: 7px 16px;
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--muted);
  cursor: pointer;
}
.unit-toggle button.active { background: var(--accent); color: #fff; }

.btn-primary {
  display: inline-block;
  background: var(--accent);
  color: #fff;
  border: 0;
  border-radius: 10px;
  font-size: 1rem;
  font-weight: 700;
  padding: 12px 26px;
  cursor: pointer;
  margin-top: 16px;
}
.btn-primary:hover { background: var(--accent-dark); }

/* ---------- result ---------- */
.result {
  display: none;
  margin-top: 18px;
  border-radius: var(--radius);
  background: linear-gradient(135deg, #eef2ff, #f5f3ff);
  border: 1px solid #dfe3ff;
  padding: 20px 22px;
}
.result.show { display: block; }
.result .big {
  font-size: clamp(1.7rem, 5vw, 2.6rem);
  font-weight: 800;
  color: var(--accent-dark);
  letter-spacing: -0.02em;
  line-height: 1.1;
}
.result .big small { font-size: 1rem; font-weight: 600; color: var(--muted); }
.result .alt { color: var(--muted); font-size: 0.95rem; margin-top: 2px; }
.breakdown {
  margin-top: 14px;
  border-top: 1px solid #d8dcef;
  padding-top: 12px;
}
.breakdown h3 { margin: 0 0 6px; font-size: 0.9rem; color: var(--ink); }
.breakdown ul { margin: 0; padding-left: 18px; font-size: 0.92rem; color: #333f5c; }
.breakdown li { margin: 3px 0; }
.note-warn {
  margin-top: 12px;
  font-size: 0.85rem;
  color: var(--warn);
  background: #fffbeb;
  border: 1px solid #fde68a;
  border-radius: 9px;
  padding: 8px 12px;
}
.price-line {
  margin-top: 12px;
  border-top: 1px solid #d8dcef;
  padding-top: 10px;
  font-size: 0.95rem;
}
.price-line strong { color: var(--accent-dark); font-size: 1.05rem; }

/* ---------- copy / share ---------- */
.result-actions { display: flex; gap: 10px; margin-top: 12px; flex-wrap: wrap; }
.btn-ghost {
  padding: 8px 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--card);
  color: var(--ink);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: border-color .15s, color .15s;
}
.btn-ghost:hover { border-color: var(--accent); color: var(--accent-dark); }

/* ---------- content sections ---------- */
.section { margin: 34px 0; }
.section h2 { font-size: 1.3rem; letter-spacing: -0.01em; margin: 0 0 10px; }
.section h3 { font-size: 1.02rem; margin: 18px 0 6px; }
.section p { color: #2c3852; }
.formula-box {
  background: #0f172a;
  color: #e2e8f0;
  border-radius: 10px;
  padding: 14px 18px;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.9rem;
  overflow-x: auto;
  margin: 10px 0;
  white-space: pre-wrap;
}
table.data { width: 100%; border-collapse: collapse; font-size: 0.92rem; margin: 10px 0; }
table.data th, table.data td {
  border: 1px solid var(--line);
  padding: 8px 10px;
  text-align: left;
}
table.data th { background: var(--accent-soft); font-weight: 700; }
table.data tr:nth-child(even) td { background: #fbfcfe; }

/* ---------- faq ---------- */
.faq-item { border-bottom: 1px solid var(--line); padding: 14px 0; }
.faq-item h3 { margin: 0 0 6px; font-size: 1rem; }
.faq-item p { margin: 0; color: #2c3852; }

/* ---------- related cards ---------- */
.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 14px; margin: 16px 0; }
.card {
  display: block;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 16px 18px;
  text-decoration: none;
  color: var(--ink);
  transition: border-color 0.15s, transform 0.15s;
}
.card:hover { border-color: var(--accent); transform: translateY(-2px); }
.card .t { font-weight: 700; margin-bottom: 4px; }
.card .d { font-size: 0.86rem; color: var(--muted); }

/* ---------- misc ---------- */
.tag {
  display: inline-block;
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--accent-dark);
  background: var(--accent-soft);
  border-radius: 999px;
  padding: 3px 10px;
  margin-bottom: 10px;
}
kbd {
  background: #eef2f7;
  border: 1px solid #cbd5e1;
  border-radius: 5px;
  padding: 0 6px;
  font-size: 0.85em;
}

@media (max-width: 560px) {
  .calc-card { padding: 16px; border-radius: 12px; }
  .fields { grid-template-columns: 1fr 1fr; gap: 10px; }
  .field input, .field select { font-size: 16px; padding: 11px 10px; }
  .field .hint { font-size: 0.7rem; }
  .btn-primary { width: 100%; }
  .unit-toggle { width: 100%; }
  .unit-toggle button { flex: 1; padding: 10px 8px; }
  .hero { padding: 24px 0 6px; }
  .hero h1 { font-size: 1.55rem; }
  .site-header .wrap { padding: 8px 16px; }
  .brand { font-size: 1.05rem; }
  .top-nav { overflow-x: auto; -webkit-overflow-scrolling: touch; max-width: 100%; }
  .top-nav a { padding: 6px 8px; font-size: 0.8rem; white-space: nowrap; }
  .result .big { font-size: 1.7rem; }
  .result { padding: 16px; }
  .cards { grid-template-columns: 1fr; }
  .formula-box { font-size: 0.78rem; padding: 12px 12px; }
  table.data { font-size: 0.82rem; }
  table.data th, table.data td { padding: 6px 7px; }
  .footer-grid { gap: 16px; }
}

@media (max-width: 380px) {
  .fields { grid-template-columns: 1fr; }
}

@media print {
  .site-header, .top-nav, .btn-primary, .unit-toggle { display: none; }
  .result { display: block !important; }
}