:root{
  --bg:#f6f7f9;--surface:#fff;--ink:#14213d;--muted:#5b6475;--line:#dde2ea;
  --brand:#0b5fff;--brand-ink:#fff;--band:#0f2a5c;--band-ink:#eef3ff;--accent:#ffb703;
  --ok-bg:#eaf2ff;--radius:14px;--shadow:0 6px 24px rgba(15,42,92,.10);
  --font:system-ui,-apple-system,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif;
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font:17px/1.65 var(--font)}
a{color:var(--brand)}
img,svg{max-width:100%;height:auto}
.wrap{max-width:1120px;margin:0 auto;padding:0 16px}
.skip{position:absolute;left:-999px}.skip:focus{left:16px;top:8px;background:#fff;padding:8px;z-index:9}

header.top{background:var(--band);color:var(--band-ink)}
header.top .wrap{display:flex;align-items:center;justify-content:space-between;height:56px}
.logo{color:#fff;text-decoration:none;font-weight:700;display:flex;gap:8px;align-items:center}
header.top nav a{color:var(--band-ink);text-decoration:none;margin-left:18px;font-size:15px}
header.top nav a:hover{text-decoration:underline}

.hero{background:var(--band);color:var(--band-ink);padding:28px 0 56px}
.hero .wrap{display:grid;grid-template-columns:1fr 1.05fr;gap:40px;align-items:start}
.hero h1{color:#fff;font-size:clamp(28px,4vw,42px);line-height:1.15;margin:8px 0 14px}
.hero p.lead{font-size:18px;margin:0 0 18px;color:#d7e2ff}
.hero ul{margin:0;padding-left:20px;color:#d7e2ff}
.hero ul li{margin:4px 0}
.diagram{margin-top:22px;max-width:260px}

.calc{background:var(--surface);color:var(--ink);border-radius:var(--radius);box-shadow:var(--shadow);padding:22px}
.calc h2{font-size:20px;margin:0 0 14px}
.field{margin-bottom:14px}
.field label{display:block;font-weight:600;font-size:15px;margin-bottom:6px}
.row{display:grid;grid-template-columns:1fr 110px;gap:8px}
.row3{display:grid;grid-template-columns:1fr 1fr;gap:12px}
input,select{width:100%;font:inherit;font-size:17px;padding:11px 12px;border:1px solid var(--line);border-radius:10px;background:#fff;color:var(--ink)}
input:focus,select:focus{outline:3px solid rgba(11,95,255,.25);border-color:var(--brand)}
.hint{font-size:13px;color:var(--muted);margin-top:4px}
.btn{display:inline-block;background:var(--brand);color:var(--brand-ink);border:0;border-radius:10px;padding:12px 18px;font:inherit;font-weight:700;cursor:pointer;transition:transform .15s,box-shadow .15s}
.btn:hover{transform:translateY(-1px);box-shadow:0 6px 16px rgba(11,95,255,.3)}
.btn.ghost{background:transparent;color:var(--brand);border:1px solid var(--line)}
.actions{display:flex;gap:10px;flex-wrap:wrap}
.result{margin-top:16px;background:var(--ok-bg);border-radius:12px;padding:16px;min-height:72px}
.result .big{font-size:28px;font-weight:800;line-height:1.2;word-break:break-word}
.result .units{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:6px 14px;margin-top:10px;font-size:15px}
.result .units b{font-variant-numeric:tabular-nums}
.steps{margin-top:10px;font-size:14px;color:var(--muted)}
.steps code{background:#fff;padding:1px 5px;border-radius:5px;color:var(--ink)}
.err{color:#b00020;font-weight:600}
[hidden]{display:none!important}

main section{padding:48px 0;border-bottom:1px solid var(--line)}
main section:last-child{border-bottom:0}
main h2{font-size:clamp(24px,3vw,30px);line-height:1.25;margin:0 0 14px}
main h3{font-size:20px;margin:24px 0 8px}
.split{display:grid;grid-template-columns:1fr 1fr;gap:36px;align-items:start}
.split .sticky{position:sticky;top:16px}
.formula{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius);padding:20px;text-align:center}
.formula .f{font-size:clamp(26px,4vw,36px);font-weight:800;font-family:Georgia,"Times New Roman",serif;margin:6px 0}
.formula p{margin:6px 0;color:var(--muted)}
.cards{display:grid;grid-template-columns:repeat(3,1fr);gap:16px;margin-top:18px}
.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius);padding:18px;transition:transform .15s,box-shadow .15s}
.card:hover{transform:translateY(-2px);box-shadow:var(--shadow)}
.card .ico{width:40px;height:40px;border-radius:10px;background:var(--ok-bg);display:grid;place-items:center;margin-bottom:10px}
.card h3{margin:0 0 6px;font-size:18px}
.card p{margin:0;font-size:16px}
.example{background:var(--surface);border:1px solid var(--line);border-left:4px solid var(--accent);border-radius:10px;padding:16px 18px;margin:14px 0}
.example p{margin:4px 0}
.tbl{overflow-x:auto;background:var(--surface);border:1px solid var(--line);border-radius:var(--radius)}
table{border-collapse:collapse;width:100%;font-size:15px;font-variant-numeric:tabular-nums}
th,td{padding:10px 12px;text-align:right;border-bottom:1px solid var(--line);white-space:nowrap}
th:first-child,td:first-child{text-align:left}
thead th{background:#eef2f8}
tbody tr:last-child td{border-bottom:0}
caption{caption-side:bottom;text-align:left;padding:10px 12px;color:var(--muted);font-size:14px}
details{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:14px 18px;margin:10px 0}
summary{font-weight:700;cursor:pointer}
details p{margin:10px 0 0}

footer{background:var(--band);color:var(--band-ink);padding:28px 0;font-size:15px}
footer a{color:#fff}

@media (max-width:900px){
  .hero .wrap,.split{grid-template-columns:1fr;gap:24px}
  .split .sticky{position:static}
  .cards{grid-template-columns:1fr}
  .diagram,.hero ul{display:none}
  .hero{padding:20px 0 40px}
  .hero p.lead{margin-bottom:0}
  header.top nav{display:none}
}
@media (max-width:420px){
  .row{grid-template-columns:1fr 92px}
  .row3{grid-template-columns:1fr}
  .result .units{grid-template-columns:1fr}
}