:root{
  --bg:#f7f9fb;
  --panel:#ffffff;
  --ink:#1e293b;
  --muted:#64748b;
  --accent:#0f766e;
  --accent-dark:#0b5e57;
  --line:#dbe3ea;
  --dark:#0f172a;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0;background:var(--bg);color:var(--ink);font-family:system-ui,-apple-system,'Segoe UI',Roboto,Arial,sans-serif;-webkit-font-smoothing:antialiased}
a{color:var(--accent);text-decoration:none}
a:hover{text-decoration:underline}
header{border-bottom:1px solid var(--line);background:var(--panel)}
.wrap{max-width:880px;margin:0 auto;padding:0 20px}
.nav{display:flex;align-items:center;justify-content:space-between;padding:16px 0}
.brand{font-weight:800;letter-spacing:.3px;font-size:17px;color:var(--ink)}
.brand span{color:var(--accent)}
.brand a{color:inherit;text-decoration:none}
.hero{padding:44px 0 20px;text-align:center}
h1{font-size:38px;line-height:1.1;margin:0 0 12px;font-weight:800;letter-spacing:-.5px}
.sub{color:var(--muted);max-width:620px;margin:0 auto;font-size:16px;line-height:1.5}
.card{background:var(--panel);border:1px solid var(--line);border-radius:8px;padding:28px;margin:28px 0;box-shadow:0 1px 2px rgba(15,23,42,.04)}
.step{display:flex;gap:16px;margin-bottom:26px}
.step:last-child{margin-bottom:0}
.num{flex:0 0 34px;height:34px;border-radius:50%;background:var(--accent);color:#fff;display:grid;place-items:center;font-weight:800;font-size:15px}
.step-body{flex:1;min-width:0}
.step h2.sh{margin:4px 0 4px;font-size:17px;font-weight:700;letter-spacing:0}
.hint{color:var(--muted);font-size:13px;margin-bottom:12px}
.chips{display:flex;flex-wrap:wrap;gap:8px}
.chip{padding:10px 14px;border:1px solid var(--line);background:var(--bg);color:var(--ink);border-radius:6px;cursor:pointer;font-weight:600;font-size:13px;font-family:inherit}
.chip:hover{border-color:var(--accent);color:var(--accent)}
.chip.active{background:var(--accent);color:#fff;border-color:var(--accent)}
select,input[type=number]{width:100%;padding:12px 14px;border:1px solid var(--line);background:var(--bg);border-radius:6px;font-family:inherit;font-size:15px;color:var(--ink)}
select:focus,input:focus{outline:2px solid var(--accent);outline-offset:0;border-color:var(--accent)}
.row{display:flex;gap:10px;align-items:center;flex-wrap:wrap}
.row input[type=number]{flex:1;min-width:120px}
.toggle{display:inline-flex;border:1px solid var(--line);border-radius:6px;overflow:hidden}
.toggle button{background:var(--bg);border:none;padding:10px 14px;font-weight:700;cursor:pointer;font-family:inherit;color:var(--muted);font-size:13px}
.toggle button.active{background:var(--accent);color:#fff}
.calc-btn{display:block;width:100%;background:var(--accent);color:#fff;border:none;padding:17px;font-size:15px;font-weight:800;text-transform:uppercase;letter-spacing:1.2px;cursor:pointer;border-radius:6px;margin-top:8px;font-family:inherit}
.calc-btn:hover{background:var(--accent-dark)}
.warn{background:#fff7ed;border-left:3px solid #d97706;padding:12px 14px;color:var(--ink);font-size:13px;margin-top:12px;display:none;border-radius:0 6px 6px 0;line-height:1.6}
.warn.show{display:block}
.result{background:var(--dark);color:#e2e8f0;border-radius:8px;padding:30px;margin:28px 0;display:none}
.result.show{display:block}
.result h2{margin:0 0 18px;font-size:13px;letter-spacing:2px;text-transform:uppercase;color:#94a3b8;font-weight:700}
.rstep{padding:18px 0;border-top:1px solid #283548}
.rstep:first-of-type{border-top:none;padding-top:0}
.rstep .label{font-size:11px;letter-spacing:1.5px;text-transform:uppercase;color:#94a3b8;font-weight:700;margin-bottom:6px}
.rstep .big{font-size:34px;font-weight:800;color:#fff;line-height:1.1}
.rstep .big span.unit{font-size:16px;color:#94a3b8;margin-left:6px;font-weight:600}
.rstep p{margin:6px 0 0;color:#cbd5e1;font-size:14px}
.meta{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:18px;padding-top:18px;border-top:1px solid #283548}
.meta .box{background:#1a2536;padding:14px;border-radius:6px}
.meta .label{font-size:10px;letter-spacing:1.5px;text-transform:uppercase;color:#94a3b8;font-weight:700;margin-bottom:4px}
.meta .val{font-size:18px;font-weight:700;color:#fff}
.mathwork{margin-top:18px;padding-top:18px;border-top:1px solid #283548}
.mathwork h3{margin:0 0 12px;font-size:11px;letter-spacing:1.5px;text-transform:uppercase;color:#5eead4;font-weight:700}
.mathwork ol{margin:0;padding-left:20px;color:#cbd5e1;font-size:13.5px;line-height:1.9}
.mathwork b{color:#fff}
.reset{display:inline-block;margin-top:18px;color:#cbd5e1;font-weight:700;cursor:pointer;font-size:13px;text-transform:uppercase;letter-spacing:1px;background:none;border:none;font-family:inherit}
.reset:hover{color:#5eead4}
.disclaimer{background:#eef2f6;border:1px solid var(--line);padding:18px 22px;margin:28px 0;border-radius:6px;font-size:13px;color:var(--ink);line-height:1.55}
.disclaimer strong{color:#92400e;text-transform:uppercase;letter-spacing:1px;font-size:12px}
.disclaimer a{text-decoration:underline}
.section-title{font-size:12px;letter-spacing:2px;text-transform:uppercase;color:var(--accent);font-weight:700;text-align:center;margin:56px 0 8px}
.section-title + h2{text-align:center;font-size:30px;margin:0 0 28px;font-weight:800;letter-spacing:-.3px}
details{border-bottom:1px solid var(--line);padding:18px 0}
details[open] summary{color:var(--accent)}
summary{cursor:pointer;font-weight:700;font-size:15px;list-style:none;display:flex;justify-content:space-between;align-items:center}
summary::-webkit-details-marker{display:none}
summary:after{content:"+";color:var(--accent);font-size:22px;font-weight:400;margin-left:12px}
details[open] summary:after{content:"\2212"}
details .body{padding-top:12px;color:var(--ink);line-height:1.6;font-size:14px}
.content h2{font-size:24px;margin:34px 0 12px;font-weight:800;letter-spacing:-.3px}
.content p{line-height:1.7;font-size:15px;margin:0 0 14px}
.content ul{line-height:1.7;font-size:15px}
table.chart{width:100%;border-collapse:collapse;background:var(--panel);border:1px solid var(--line);border-radius:8px;overflow:hidden;font-size:14px;margin:14px 0 6px}
table.chart th{text-align:left;padding:11px 14px;background:#eef2f6;font-size:12px;text-transform:uppercase;letter-spacing:.8px;color:var(--muted);border-bottom:1px solid var(--line)}
table.chart td{padding:11px 14px;border-bottom:1px solid var(--line)}
table.chart tr:last-child td{border-bottom:none}
.chart-note{font-size:12.5px;color:var(--muted);margin:0 0 18px}
.related{display:flex;flex-wrap:wrap;gap:10px;margin:14px 0 6px}
.related a{display:inline-block;padding:10px 16px;background:var(--panel);border:1px solid var(--line);border-radius:6px;font-weight:600;font-size:14px}
.related a:hover{border-color:var(--accent);text-decoration:none}
footer{border-top:1px solid var(--line);background:var(--panel);padding:32px 0;margin-top:60px;text-align:center;font-size:13px;color:var(--muted)}
footer .brand{margin-bottom:8px;font-size:15px}
footer nav{margin:10px 0;display:flex;gap:18px;justify-content:center;flex-wrap:wrap}
footer nav a{color:var(--muted);font-weight:600}
footer nav a:hover{color:var(--accent)}
@media (max-width:640px){
  h1{font-size:30px}
  .card{padding:20px}
  .rstep .big{font-size:28px}
  .meta{grid-template-columns:1fr}
}