:root{
  --navy:#0b2a4a;--navy2:#164a78;--gold:#d6a84b;--gold2:#f4e5b8;
  --bg:#f4f7fb;--card:#fff;--text:#142238;--muted:#5e6d85;--border:#dbe3ee;--ok:#1f7a4c
}
*{box-sizing:border-box}
body{margin:0;background:var(--bg);color:var(--text);font-family:Inter,ui-sans-serif,system-ui,-apple-system,"Segoe UI",sans-serif;line-height:1.5}
.app{width:min(1180px,100%);margin:0 auto;padding:16px}
.hero{background:linear-gradient(135deg,var(--navy),var(--navy2));color:#fff;border-radius:18px;padding:22px;margin-bottom:16px}
.eyebrow{display:inline-block;font-size:12px;font-weight:800;letter-spacing:.08em;text-transform:uppercase;color:var(--gold2);margin-bottom:6px}
.hero h1{margin:0 0 8px;font-size:clamp(22px,4vw,34px)}
.hero p{margin:0;color:rgba(255,255,255,.87);max-width:82ch}
.layout{display:grid;grid-template-columns:minmax(0,1fr) 330px;gap:16px}
.stage{background:var(--card);border:1px solid var(--border);border-radius:16px;padding:14px;min-width:0}
#board{display:block;width:100%;height:auto;border:1px solid var(--border);border-radius:12px;background:#fff;touch-action:none}
.explanation{margin:12px 0 0;padding:12px 14px;border-radius:12px;background:#eef5fb;border-left:4px solid var(--gold);font-weight:700;color:var(--navy)}
.panel{display:grid;gap:12px;align-content:start}
.card{background:var(--card);border:1px solid var(--border);border-radius:14px;padding:14px}
.metrics{display:grid;grid-template-columns:repeat(3,1fr);gap:8px}
.metrics div{display:grid;gap:2px;text-align:center;padding:8px;border-radius:10px;background:#f7f9fc}
.metrics span{font-size:13px;color:var(--muted)}
.metrics strong{font-size:18px;color:var(--navy)}
.result{display:flex;align-items:center;justify-content:space-between;gap:12px}
.result span{font-size:14px;color:var(--muted)}
.result strong{font-size:24px;color:var(--ok)}
.gold-result strong{color:#a66f00}
.controls{display:grid;gap:10px}
.check{display:flex;align-items:center;gap:10px;font-weight:650}
.check input{width:20px;height:20px;accent-color:var(--navy)}
button{border:0;border-radius:11px;padding:11px 12px;font-weight:800;cursor:pointer;min-height:44px;font-size:14px}
button:focus-visible{outline:3px solid var(--gold);outline-offset:2px}
.primary{background:var(--navy);color:#fff}
.ghost{background:#edf2f7;color:var(--navy)}
.note strong{color:var(--navy)}
.note p{margin:6px 0 0;color:var(--muted);font-size:14px}
.vertex{fill:#fff;stroke:var(--navy);stroke-width:4;cursor:grab}
.vertex:active{cursor:grabbing}
.vlabel{font-size:18px;font-weight:800;fill:var(--navy)}
.angle-label{font-size:16px;font-weight:800;fill:var(--navy)}
.ext-label{font-size:15px;font-weight:800;fill:#a66f00}
.ext-line{stroke:#9aa8ba;stroke-width:2.5;stroke-dasharray:7 6}
.int-arc{fill:none;stroke:var(--navy2);stroke-width:4}
.ext-arc{fill:none;stroke:var(--gold);stroke-width:4}
@media(max-width:860px){.layout{grid-template-columns:1fr}.panel{order:2}}
@media(max-width:420px){.app{padding:10px}.hero{padding:16px}.metrics{grid-template-columns:1fr 1fr 1fr}.result{align-items:flex-start;flex-direction:column}.result strong{font-size:22px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;transition:none!important}}