:root{
  --ink:#14213d;--muted:#60708a;--line:#d9e1ec;--paper:#fff;--soft:#f6f8fb;
  --blue:#315f9c;--red:#a51c30;--green:#2f7d5a;--gold:#b57912;--violet:#6652a3;
  --train:#2f7d5a;--valid:#315f9c;--test:#a51c30;--audit:#7652a3;
  --shadow:0 12px 30px rgba(20,33,61,.08);--radius:18px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:#fff;color:var(--ink);font:16px/1.55 Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif}
a{color:var(--blue)}button,input,select{font:inherit}.container{width:min(1200px,calc(100% - 30px));margin:auto}
.site-header{position:sticky;top:0;z-index:20;background:rgba(255,255,255,.96);border-bottom:1px solid var(--line);backdrop-filter:blur(12px)}
.nav-shell{min-height:64px;display:flex;align-items:center;justify-content:space-between;gap:18px}.brand{display:flex;align-items:center;gap:10px;text-decoration:none;color:var(--ink);font-weight:850}.brand-mark{display:grid;place-items:center;width:42px;height:42px;border-radius:12px;background:var(--ink);color:#fff;font-size:13px;letter-spacing:.08em}.site-nav{display:flex;flex-wrap:wrap;justify-content:flex-end;gap:4px}.site-nav a{padding:8px 10px;border-radius:10px;text-decoration:none;color:#45516a;font-size:13px}.site-nav a:hover,.site-nav a.active{background:#eef2f8;color:var(--ink)}
.hero{background:linear-gradient(180deg,#f3f7fc 0%,#fff 100%);border-bottom:1px solid var(--line);padding:38px 0 30px}.hero h1{font-size:clamp(30px,5vw,52px);line-height:1.03;margin:6px 0 12px;letter-spacing:-.04em}.hero p{max-width:900px;color:var(--muted);font-size:18px;margin:0}.kicker{font-size:13px!important;font-weight:850;text-transform:uppercase;letter-spacing:.13em;color:var(--blue)!important}.pills,.legend,.button-row,.steps{display:flex;flex-wrap:wrap;gap:8px}.pills{margin-top:18px}.pill,.step{border:1px solid var(--line);background:#fff;border-radius:999px;padding:7px 10px;font-size:13px;color:#526078}.step.active{background:var(--ink);color:#fff;border-color:var(--ink)}
main{padding:28px 0 52px}.notice,.prompt,.callout,.explain{border-radius:14px;padding:14px 16px}.notice{background:#f7f9fc;border:1px solid var(--line)}.prompt{background:#fff7e7;border:1px solid #ecd4a1}.callout{background:#eef4fb;border:1px solid #d7e2f1}.explain{background:#f7f9fc;border:1px solid var(--line)}.small{font-size:13px;color:var(--muted)}.meta{font-size:12px;text-transform:uppercase;letter-spacing:.11em;color:var(--muted);font-weight:850}
.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px}.card,.panel{background:var(--paper);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow)}.card{padding:22px}.card h2{margin:5px 0 8px;font-size:22px}.card p{color:#5c6880}.card-link,.btn{display:inline-flex;align-items:center;justify-content:center;min-height:44px;padding:9px 14px;border-radius:11px;border:1px solid var(--ink);background:var(--ink);color:#fff;text-decoration:none;font-weight:780;cursor:pointer}.btn.secondary{background:#fff;color:var(--ink);border-color:var(--line)}.btn.warn{background:#fff5f5;color:#8d2130;border-color:#e9c6cc}.btn.good{background:#eef8f2;color:#246748;border-color:#b8dac6}.btn:disabled{opacity:.45;cursor:not-allowed}
.activity-layout{display:grid;grid-template-columns:minmax(0,1.65fr) minmax(300px,.78fr);gap:18px;margin-top:16px}.panel{padding:18px;min-width:0}.panel h2{font-size:20px;margin:0 0 14px}.canvas-wrap{position:relative;border:1px solid var(--line);border-radius:14px;overflow:hidden;background:#fff}.canvas-wrap canvas{display:block;width:100%;height:auto;touch-action:none}.legend{margin:10px 0 0;color:var(--muted);font-size:13px}.legend span{display:flex;align-items:center;gap:6px}.swatch{width:11px;height:11px;border-radius:3px;display:inline-block}.controls{display:grid;align-content:start;gap:14px}.control{display:grid;gap:6px}.control label{font-size:13px;font-weight:800;color:#49566e}.control input[type=range]{width:100%;accent-color:var(--ink)}.control select,.control input[type=number]{width:100%;padding:10px 11px;border:1px solid #cfd7e4;border-radius:10px;background:#fff;color:var(--ink)}.value{float:right;color:var(--blue);font-variant-numeric:tabular-nums}
.stat-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:9px}.stat{padding:12px;border:1px solid var(--line);border-radius:12px;background:#fafbfd}.stat .label{display:block;font-size:11px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);font-weight:850}.stat .num{display:block;font-size:22px;font-weight:900;margin-top:2px;font-variant-numeric:tabular-nums}.reveal{border:1px solid var(--line);border-radius:12px;margin-top:12px;overflow:hidden}.reveal summary{padding:11px 13px;cursor:pointer;font-weight:800;background:#fafbfd}.reveal-body{padding:12px 14px;color:#4f5b71}.footer{border-top:1px solid var(--line);padding:24px 0 38px;color:var(--muted);font-size:13px}
.metric-table{width:100%;border-collapse:collapse;font-size:14px}.metric-table th,.metric-table td{border-bottom:1px solid var(--line);padding:9px 8px;text-align:right}.metric-table th:first-child,.metric-table td:first-child{text-align:left}.metric-table tr.selected{background:#eef4fb}.metric-table tr.best{outline:2px solid rgba(49,95,156,.22);outline-offset:-2px}.metric-table button{font:inherit;border:1px solid var(--line);border-radius:8px;background:#fff;padding:5px 8px;cursor:pointer}.metric-table button:hover{background:#f4f7fb}
.splitbar{display:flex;height:64px;border-radius:12px;overflow:hidden;border:1px solid var(--line);margin:12px 0}.splitbar>div{display:grid;place-items:center;text-align:center;font-weight:850;font-size:13px}.train{background:#eaf5ef;color:#226849}.valid{background:#edf3fb;color:#254f82}.test{background:#fff0f1;color:#8a2531}.audit{background:#f2edfb;color:#5e438e}.status{padding:11px 12px;border-radius:11px;font-weight:750;font-size:14px}.status.good{background:#eaf5ef;color:#226849}.status.bad{background:#fff0f1;color:#8a2531}.status.neutral{background:#f2f4f8;color:#526078}.status.warn{background:#fff7e7;color:#7b5a13}.quiz-options{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:9px}.quiz-options button{min-height:54px;padding:9px;border:1px solid var(--line);border-radius:12px;background:#fff;font-weight:800;color:var(--ink);cursor:pointer}.quiz-options button.correct{background:#eaf5ef;border-color:#9bc9ad}.quiz-options button.wrong{background:#fff0f1;border-color:#e0aab1}
.tab-row{display:flex;gap:6px;flex-wrap:wrap}.tab-row button{border:1px solid var(--line);background:#fff;border-radius:999px;padding:8px 12px;cursor:pointer;font-weight:750;color:#536078}.tab-row button.active{background:var(--ink);color:#fff;border-color:var(--ink)}.formula{font-family:ui-monospace,SFMono-Regular,Menlo,monospace;background:#f6f8fb;border:1px solid var(--line);padding:12px 14px;border-radius:12px;overflow:auto}.fold-row{display:grid;grid-template-columns:repeat(var(--k),minmax(0,1fr));gap:5px;margin:10px 0}.fold{padding:10px 4px;border-radius:10px;border:1px solid var(--line);text-align:center;font-size:12px;font-weight:800}.fold.hold{background:#fff0f1;border-color:#e0aab1;color:#8a2531}.fold.keep{background:#edf3fb;color:#254f82}.progress{height:11px;background:#edf1f6;border-radius:999px;overflow:hidden}.progress>div{height:100%;background:var(--blue);width:0}.badge{display:inline-flex;align-items:center;gap:5px;border-radius:999px;padding:4px 8px;background:#f1f4f8;color:#526078;font-size:12px;font-weight:800}.badge.good{background:#eaf5ef;color:#226849}.badge.bad{background:#fff0f1;color:#8a2531}.center{text-align:center}.hr{height:1px;background:var(--line);margin:16px 0}.tight{margin:0}.subtle{color:var(--muted)}
@media(max-width:900px){.nav-shell{align-items:flex-start;padding:10px 0}.site-nav{display:none}.activity-layout,.grid{grid-template-columns:1fr}.hero{padding-top:28px}.quiz-options{grid-template-columns:1fr}.stat-grid{grid-template-columns:1fr 1fr}}
@media(max-width:500px){.container{width:min(100% - 18px,1200px)}.panel,.card{padding:14px}.hero p{font-size:16px}.stat-grid{grid-template-columns:1fr}.button-row .btn{flex:1}.splitbar{height:78px}.metric-table{font-size:12px}.metric-table th,.metric-table td{padding:7px 5px}}