:root{
    --diskA:#4f7cac;
    --diskB:#b86a6a;
    --big:#665d8a;
    --accent:#c89b3c;
    --good:#4e9b74;
  }
  header{margin-bottom:38px;}
  .eyebrow{font-family:'Space Mono',monospace;font-size:12px;letter-spacing:0.32em;text-transform:uppercase;color:var(--accent);margin-bottom:14px;}
  h1{font-family:'Merriweather',serif;font-weight:500;font-size:clamp(32px,5vw,52px);line-height:1.04;letter-spacing:-0.02em;max-width:20ch;}
  h1 em{font-style:italic;color:var(--big);}
  .sub{color:var(--muted);font-size:18px;line-height:1.6;max-width:64ch;margin-top:18px;}
  .sub b{color:var(--good);font-weight:500;}

  .layout{display:grid;grid-template-columns:1.35fr 1fr;gap:28px;margin-top:42px;align-items:start;}
  @media(max-width:860px){.layout{grid-template-columns:1fr;}}

  .stage{background:var(--panel);border:1px solid var(--line);border-radius:20px;padding:14px;position:relative;overflow:hidden;}
  .stage::before{content:"";position:absolute;inset:0;background:none;pointer-events:none;}
  canvas{width:100%;height:480px;display:block;border-radius:12px;cursor:grab;}
  canvas:active{cursor:grabbing;}
  .hint{position:absolute;bottom:20px;left:0;right:0;text-align:center;font-family:'Space Mono',monospace;font-size:11px;letter-spacing:0.12em;color:var(--faint);text-transform:uppercase;pointer-events:none;}
  .status{position:absolute;top:22px;left:24px;font-family:'Space Mono',monospace;font-size:13px;letter-spacing:0.12em;color:var(--muted);text-transform:uppercase;pointer-events:none;}
  .status b{color:var(--good);}

  .side{display:flex;flex-direction:column;gap:18px;}

  .controls{background:var(--panel);border:1px solid var(--line);border-radius:18px;padding:24px;}
  .ctrl-row{display:flex;align-items:center;justify-content:space-between;margin-bottom:6px;}
  .ctrl-label{font-family:'Space Mono',monospace;font-size:12px;letter-spacing:0.1em;color:var(--muted);text-transform:uppercase;}
  .ctrl-val{font-family:'Space Mono',monospace;font-size:15px;color:var(--big);}
  input[type=range]{-webkit-appearance:none;appearance:none;width:100%;height:4px;border-radius:4px;background:var(--panel-raised);outline:none;margin:8px 0 16px;}
  input[type=range]::-webkit-slider-thumb{-webkit-appearance:none;width:18px;height:18px;border-radius:50%;background:#fff;border:3px solid var(--big);cursor:pointer;}
  input[type=range]::-moz-range-thumb{width:18px;height:18px;border-radius:50%;background:#fff;border:3px solid var(--big);cursor:pointer;}
  .btns{display:flex;gap:10px;}
  .btns button{flex:1;font-family:'DM Sans',sans-serif;font-size:12px;font-weight:700;letter-spacing:0.08em;text-transform:uppercase;color:var(--ink);background:transparent;border:1px solid var(--line);border-radius:8px;padding:11px 6px;cursor:pointer;transition:all .18s ease;}
  .btns button:hover{border-color:var(--big);background:rgba(102,93,138,0.10);}
  .btns button.active{border-color:var(--good);color:var(--good);background:rgba(78,155,116,0.08);}

  .legend{display:flex;flex-direction:column;gap:12px;background:var(--panel);border:1px solid var(--line);border-radius:18px;padding:22px 24px;}
  .leg-item{display:flex;align-items:center;gap:12px;}
  .dot{width:13px;height:13px;border-radius:50%;flex-shrink:0;}
  .leg-text{font-size:15px;color:var(--ink);}
  .leg-text span{color:var(--muted);font-size:13px;display:block;margin-top:1px;}

  .factcard{background:var(--panel);border:1px solid var(--line);border-radius:18px;padding:22px 24px;}
  .factcard .fc-title{font-family:'Merriweather',serif;font-size:19px;color:var(--big);margin-bottom:10px;}
  .fc-row{display:flex;justify-content:space-between;align-items:baseline;padding:8px 0;border-top:1px solid var(--line);}
  .fc-row .k{font-family:'Space Mono',monospace;font-size:12px;letter-spacing:0.04em;color:var(--muted);text-transform:uppercase;}
  .fc-row .v{font-family:'Space Mono',monospace;font-size:14px;color:var(--ink);}
  .fc-note{color:var(--faint);font-size:12.5px;line-height:1.5;margin-top:14px;font-style:italic;}

  .concept{margin-top:48px;}
  .concept h2{font-family:'Merriweather',serif;font-weight:500;font-size:26px;margin-bottom:24px;letter-spacing:-0.01em;}
  .steps{display:grid;grid-template-columns:repeat(3,1fr);gap:20px;}
  @media(max-width:780px){.steps{grid-template-columns:1fr;}}
  .step{background:var(--panel);border:1px solid var(--line);border-radius:16px;padding:26px;}
  .step-num{font-family:'Space Mono',monospace;font-size:13px;color:var(--accent);letter-spacing:0.1em;margin-bottom:14px;}
  .step h3{font-family:'Merriweather',serif;font-weight:500;font-size:19px;margin-bottom:10px;color:var(--big);}
  .step p{color:var(--muted);font-size:15px;line-height:1.62;}
  .step .eq{font-family:'Space Mono',monospace;font-size:13.5px;color:var(--ink);background:rgba(255,255,255,0.04);border-radius:8px;padding:10px 12px;margin-top:14px;border:1px solid var(--line);}

  .result{margin-top:42px;background:var(--panel);border:1px solid var(--line);border-radius:18px;padding:32px;}
  .result .label{font-family:'Space Mono',monospace;font-size:12px;letter-spacing:0.18em;text-transform:uppercase;color:var(--diskA);margin-bottom:14px;}
  .result .derive{font-family:'Space Mono',monospace;font-size:14px;color:var(--muted);line-height:1.9;margin-bottom:22px;}
  .result .derive b{color:var(--ink);}
  .optgrid{display:grid;grid-template-columns:repeat(2,1fr);gap:14px;}
  @media(max-width:600px){.optgrid{grid-template-columns:1fr;}}
  .opt{border:1px solid var(--line);border-radius:12px;padding:16px 18px;display:flex;align-items:center;gap:14px;}
  .opt .tag{font-family:'Merriweather',serif;font-size:20px;color:var(--muted);}
  .opt .ex{font-family:'Space Mono',monospace;font-size:14px;color:var(--ink);}
  .opt.correct{border-color:var(--good);background:rgba(78,155,116,0.08);}
  .opt.correct .tag{color:var(--good);}
  .opt.correct .ex{color:var(--good);}