:root {
  --bg: #f6f8fb;
  --surface: #ffffff;
  --text: #1a2233;
  --muted: #5b6678;
  --accent: #2451e0;
  --accent-dark: #1a3cad;
  --border: #e3e8f0;
  --radius: 14px;
  --shadow: 0 1px 2px rgba(16, 24, 40, .05), 0 4px 16px rgba(16, 24, 40, .06);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  font-size: 17px;
}

.container { max-width: 860px; margin: 0 auto; padding: 0 16px; }

/* Header */
.site-header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding-top: 12px;
  padding-bottom: 12px;
  flex-wrap: wrap;
}
.logo {
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--text);
  text-decoration: none;
  white-space: nowrap;
}
.site-nav { display: flex; gap: 18px; flex-wrap: wrap; }
.site-nav a { color: var(--muted); text-decoration: none; font-size: .95rem; }
.site-nav a:hover { color: var(--accent); }

/* Typography */
h1 { font-size: 1.7rem; line-height: 1.25; margin: 24px 0 8px; }
h2 { font-size: 1.25rem; margin: 32px 0 8px; }
.lead { color: var(--muted); margin-top: 0; }
a { color: var(--accent); }
main { padding-bottom: 48px; }

.breadcrumbs { font-size: .85rem; color: var(--muted); margin-top: 16px; }
.breadcrumbs a { color: var(--muted); }
.breadcrumbs span { margin: 0 2px; }

/* Cards */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 14px; margin: 16px 0; }
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}
.tool-card {
  display: flex;
  gap: 12px;
  padding: 16px;
  text-decoration: none;
  color: var(--text);
  transition: transform .12s ease, border-color .12s ease;
}
.tool-card:hover { transform: translateY(-2px); border-color: var(--accent); }
.tool-icon { font-size: 1.6rem; line-height: 1; }
.tool-card-body { display: flex; flex-direction: column; gap: 4px; }
.tool-card-body strong { font-size: 1rem; }
.tool-card-body span { color: var(--muted); font-size: .88rem; line-height: 1.45; }

/* Calculator form */
.calc {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px;
  margin: 20px 0;
}
.calc .row { display: flex; flex-wrap: wrap; gap: 14px; margin-bottom: 14px; }
.calc .field { flex: 1 1 180px; display: flex; flex-direction: column; gap: 6px; }
.calc label { font-size: .88rem; font-weight: 600; color: var(--muted); }
.calc input[type="number"], .calc input[type="date"], .calc input[type="text"], .calc select {
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  font-size: 1.05rem;
  font-family: inherit;
  background: #fbfcfe;
  color: var(--text);
  width: 100%;
}
.calc input:focus, .calc select:focus { outline: 2px solid var(--accent); outline-offset: 0; border-color: var(--accent); }
.calc .radio-group { display: flex; gap: 14px; flex-wrap: wrap; align-items: center; }
.calc .radio-group label { font-weight: 400; color: var(--text); font-size: .95rem; display: flex; align-items: center; gap: 6px; }
.btn {
  display: inline-block;
  background: var(--accent);
  color: #fff;
  border: 0;
  border-radius: 10px;
  padding: 12px 22px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  font-family: inherit;
}
.btn:hover { background: var(--accent-dark); }

.result {
  margin-top: 16px;
  padding: 16px;
  border-radius: 10px;
  background: #eef3ff;
  border: 1px solid #d6e0fb;
  display: none;
}
.result.show { display: block; }
.result .big { font-size: 1.45rem; font-weight: 700; }
.result table { width: 100%; border-collapse: collapse; margin-top: 8px; }
.result td { padding: 6px 4px; border-bottom: 1px solid #dbe4fa; font-size: .95rem; }
.result td:last-child { text-align: right; font-weight: 600; white-space: nowrap; }
.result tr:last-child td { border-bottom: 0; }

/* Content sections */
.content-block { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 4px 20px 12px; margin: 20px 0; }
.content-block h2 { margin-top: 20px; }
.content-block table { width: 100%; border-collapse: collapse; margin: 12px 0; font-size: .95rem; }
.content-block th, .content-block td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--border); }
.content-block th { color: var(--muted); font-size: .85rem; }
.formula {
  background: #f1f4f9;
  border-radius: 8px;
  padding: 10px 14px;
  font-family: ui-monospace, "Cascadia Mono", Consolas, monospace;
  font-size: .95rem;
  overflow-x: auto;
}

/* FAQ */
.faq-item { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; margin: 8px 0; padding: 0 16px; }
.faq-item summary { cursor: pointer; font-weight: 600; padding: 12px 0; }
.faq-a { padding: 0 0 14px; color: var(--muted); }

/* Related */
.related h2 { margin-top: 40px; }

/* Hero (home) */
.hero { text-align: center; padding: 40px 0 8px; }
.hero h1 { font-size: 2rem; margin: 0 0 10px; }
.hero p { color: var(--muted); max-width: 560px; margin: 0 auto; }

.cluster-nav {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  justify-content: center;
  margin: 18px 0 26px;
}
.cluster-nav a {
  color: var(--accent);
  background: #eef3ff;
  border: 1px solid #d6e0fb;
  border-radius: 999px;
  padding: 7px 12px;
  text-decoration: none;
  font-size: .9rem;
  font-weight: 600;
}
.cluster-nav a:hover { border-color: var(--accent); background: #e4ecff; }
.tool-group { margin: 34px 0 10px; scroll-margin-top: 72px; }
.tool-group-head h2 { margin-bottom: 4px; }
.tool-group-head p { margin: 0 0 12px; color: var(--muted); }

/* Footer */
.site-footer { border-top: 1px solid var(--border); background: var(--surface); }
.footer-inner { padding: 20px 16px; color: var(--muted); font-size: .88rem; }
.footer-inner p { margin: 4px 0; }

@media (max-width: 600px) {
  h1 { font-size: 1.45rem; }
  .hero h1 { font-size: 1.6rem; }
  body { font-size: 16px; }
}