:root{
  color-scheme:light;
  --bg:#f8fafc;--surface:#ffffff;--text:#0f172a;--muted:#475569;--line:#d9e2ef;
  --brand:#2563eb;--brand-d:#1d4ed8;--brand-2:#0891b2;--accent:#eff6ff;--field:#ffffff;
  --res-a:#047857;--res-b:#059669;
  --warn:#b45309;--warn-bg:#fffbeb;--focus:#2563eb;--on-brand:#fff;
  --hero:linear-gradient(180deg,#dbeafe 0%,#f8fafc 100%);
  --radius:16px;--shadow:0 1px 2px rgba(15,23,42,.06),0 10px 30px rgba(37,99,235,.10);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth;-webkit-text-size-adjust:100%}
body{margin:0;background:var(--hero) top/100% 460px no-repeat,var(--bg);color:var(--text);
  font:17px/1.7 Inter,system-ui,-apple-system,"Segoe UI",Roboto,Arial,sans-serif}
img,svg{max-width:100%;height:auto}
a{color:var(--brand);text-underline-offset:3px}a:hover{color:var(--brand-d)}
:focus-visible{outline:3px solid var(--focus);outline-offset:2px;border-radius:6px}
.skip{position:absolute;left:-999px;top:0;background:var(--brand);color:var(--on-brand);padding:.6rem 1rem;z-index:10;border-radius:0 0 8px 0}
.skip:focus{left:0}
.wrap{max-width:980px;margin:0 auto;padding:0 18px}
.narrow{max-width:760px}

/* Header */
header.site{background:var(--surface);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:5}
header.site .wrap{display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;gap:6px 20px;padding-top:10px;padding-bottom:10px}
.brand{display:flex;align-items:center;gap:10px;font-weight:800;font-size:1.15rem;color:var(--text);text-decoration:none;letter-spacing:-.01em}
.brand svg{flex:none}
nav ul{display:flex;flex-wrap:wrap;gap:2px 6px;list-style:none;margin:0;padding:0}
nav a{display:block;color:var(--muted);text-decoration:none;font-size:.95rem;font-weight:500;padding:7px 12px;border-radius:999px}
nav a:hover{background:var(--accent);color:var(--brand-d)}
nav a[aria-current="page"]{background:var(--accent);color:var(--brand-d);font-weight:700}

/* Hero */
.hero{padding:44px 0 6px;text-align:center}
.hero h1{font-size:clamp(2rem,5vw,3rem);line-height:1.12;margin:0 0 14px;letter-spacing:-.025em;font-weight:800}
.hero h1 span{background:linear-gradient(90deg,var(--brand),var(--brand-2));-webkit-background-clip:text;background-clip:text;color:transparent}
.hero p{color:var(--muted);max-width:620px;margin:0 auto;font-size:1.06rem}
.byline{font-size:.86rem!important;color:var(--muted);margin-top:16px!important}

/* Calculator card */
.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow);padding:26px}
.calc{margin:26px 0 8px}
fieldset{border:0;margin:0 0 22px;padding:0}
legend{font-weight:700;margin-bottom:10px;padding:0}
.step-n{display:inline-grid;place-items:center;width:24px;height:24px;border-radius:50%;background:var(--brand);color:var(--on-brand);font-size:.8rem;font-weight:800;margin-right:8px}
.modes{display:grid;grid-template-columns:repeat(3,1fr);gap:6px;background:var(--accent);padding:5px;border-radius:14px}
.modes input{position:absolute;opacity:0;pointer-events:none}
.modes label{display:block;text-align:center;padding:12px 6px;border-radius:10px;cursor:pointer;font-size:.95rem;font-weight:700;line-height:1.25;color:var(--muted);transition:background .15s,color .15s}
.modes label:hover{color:var(--brand-d)}
.modes input:checked+label{background:var(--surface);color:var(--brand-d);box-shadow:0 1px 3px rgba(15,23,42,.15),inset 0 0 0 2px var(--brand)}
.modes input:focus-visible+label{outline:3px solid var(--focus);outline-offset:2px}
.grid{display:grid;gap:18px;grid-template-columns:1fr}
@media (min-width:760px){.grid{grid-template-columns:1fr 1fr 1fr}}
.field label{display:block;font-weight:700;font-size:.95rem;margin-bottom:6px}
.field .hint{display:block;font-size:.83rem;color:var(--muted);margin-top:6px;line-height:1.45}
.input{display:flex;align-items:center;border:2px solid var(--line);border-radius:12px;background:var(--field);overflow:hidden;transition:border-color .15s,box-shadow .15s}
.input:hover{border-color:#93b4f5}
.input:focus-within{border-color:var(--brand);box-shadow:0 0 0 4px rgba(37,99,235,.18)}
.input .pre{padding:0 0 0 14px;color:var(--muted);font-weight:700;white-space:nowrap}
.input input{flex:1;min-width:0;border:0;background:transparent;color:var(--text);font:inherit;font-size:1.15rem;padding:13px 14px;outline:0}
.input input::placeholder{color:#8492a8;opacity:1}
.input.result{background:#ecfdf5;border-color:var(--res-b);border-style:dashed}
.input.result input{font-weight:800;color:var(--res-a)}

.row{display:flex;flex-wrap:wrap;gap:10px;align-items:center;margin-top:22px}
.btn{font:inherit;font-weight:700;padding:12px 20px;border-radius:12px;border:2px solid var(--line);background:var(--surface);color:var(--text);cursor:pointer;transition:transform .05s,border-color .15s,background .15s}
.btn:hover{border-color:var(--brand)}
.btn:active{transform:translateY(1px)}
.btn.primary{background:var(--brand);border-color:var(--brand);color:var(--on-brand)}
.btn.primary:hover{background:var(--brand-d);border-color:var(--brand-d)}
.cur{margin-left:auto;display:flex;align-items:center;gap:8px;font-size:.93rem;font-weight:600}
.cur select{font:inherit;font-weight:600;padding:10px 12px;border-radius:10px;border:2px solid var(--line);background:var(--field);color:var(--text)}
.error{color:var(--warn);background:var(--warn-bg);font-weight:600;margin:16px 0 0;padding:0;border-radius:10px;font-size:.95rem}
.error:not(:empty){padding:10px 14px}

/* Big result panel */
.result-box{margin-top:20px;padding:20px 22px;border-radius:14px;color:#fff;
  background:linear-gradient(135deg,var(--res-a) 0%,var(--res-b) 100%);display:flex;flex-wrap:wrap;align-items:baseline;justify-content:space-between;gap:6px 16px}
.result-box .rl{font-size:.9rem;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.95}
.result-box strong{font-size:clamp(1.8rem,6vw,2.6rem);line-height:1.1;font-weight:800;letter-spacing:-.02em;word-break:break-word}
.steps{margin-top:14px;padding:14px 16px;background:var(--accent);border-radius:12px;font-size:.95rem;color:var(--text)}
.steps:empty{display:none}
.steps b{display:block;margin-bottom:2px;color:var(--brand-d)}
.steps code{word-break:break-word;font-family:ui-monospace,Consolas,monospace}

/* Content */
main h2{font-size:1.6rem;line-height:1.25;margin:52px 0 12px;letter-spacing:-.015em}
main h3{font-size:1.2rem;margin:28px 0 6px}
table{width:100%;border-collapse:separate;border-spacing:0;margin:18px 0;font-size:.95rem;display:block;overflow-x:auto;border:1px solid var(--line);border-radius:12px;background:var(--surface)}
th,td{border-bottom:1px solid var(--line);padding:12px 14px;text-align:left}
tr:last-child td{border-bottom:0}
th{background:var(--accent);font-weight:700}
.formula{background:var(--accent);border-left:4px solid var(--brand);padding:12px 18px;border-radius:0 12px 12px 0;margin:12px 0;font-family:ui-monospace,Consolas,monospace;font-size:.96rem;overflow-x:auto;font-weight:600}
details{border:1px solid var(--line);border-radius:12px;background:var(--surface);margin:10px 0;padding:0 18px}
details[open]{border-color:var(--brand)}
summary{cursor:pointer;font-weight:700;padding:15px 0}
details[open] summary{border-bottom:1px solid var(--line);margin-bottom:12px}
details p{margin-top:0}
.note{font-size:.9rem;color:var(--muted);background:var(--surface);border:1px dashed var(--line);border-radius:12px;padding:12px 16px;margin:22px 0}
.crumbs{font-size:.88rem;color:var(--muted);margin:22px 0 0}
.crumbs a{color:var(--muted)}
.tldr{background:var(--accent);border:1px solid var(--line);border-radius:var(--radius);padding:16px 20px;margin:20px 0}
.tldr p{margin:0}

footer.site{margin-top:72px;background:var(--surface);border-top:1px solid var(--line);font-size:.92rem;color:var(--muted)}
footer.site .wrap{padding-top:28px;padding-bottom:28px}
footer.site ul{list-style:none;padding:0;margin:0 0 14px;display:flex;flex-wrap:wrap;gap:6px 20px}
footer.site a{color:var(--muted)}footer.site a:hover{color:var(--brand-d)}
footer.site p{margin:.4rem 0}

@media (max-width:520px){
  header.site{position:static}
  nav a{padding:6px 9px;font-size:.9rem}
  body{font-size:16px}
  .card{padding:18px}
  .modes label{font-size:.85rem;padding:11px 4px}
  .cur{margin-left:0;width:100%}
  .btn{flex:1}
}
@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}*{transition:none!important}}
@media print{header.site,footer.site,.row,.modes{display:none}}