/* ── page shell ── */
    body {
      flex-direction: column;
      padding: 20px;
      gap: 16px;
      min-height: 100vh;
      display: flex;
      align-items: stretch;
      justify-content: flex-start;
      /* re-apply gradient since style.css body rules can fight each other */
      background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    }

    h2 {
      text-align: center;
      color: white;
      font-size: 28px;
      text-shadow: 2px 2px 4px rgba(0,0,0,.2);
      margin-bottom: 4px;
    }
    .subtitle {
      text-align: center;
      color: rgba(255,255,255,.65);
      font-size: 13px;
      margin-bottom: 12px;
    }

    /* ── layout ── */
    .layout {
      display: flex;
      gap: 20px;
      flex: 1;
      align-items: stretch;
      min-height: 0;
    }

    /* ── sidebar ── */
    .controls {
      flex: 0 0 250px;
      background: rgba(255,255,255,.95);
      padding: 20px;
      border-radius: 12px;
      box-shadow: 0 8px 16px rgba(0,0,0,.3);
      display: flex;
      flex-direction: column;
      gap: 0;
    }

    .control-group {
      margin-bottom: 16px;
      padding-bottom: 14px;
      border-bottom: 2px solid #e5e7eb;
    }
    .control-group:last-child {
      border-bottom: none;
      margin-bottom: 0;
      padding-bottom: 0;
    }
    .control-group h3 {
      color: #6b21a8;
      margin-bottom: 10px;
      font-size: 15px;
    }

    label {
      display: block;
      color: #4b5563;
      font-size: 13px;
      font-weight: 500;
      margin-bottom: 6px;
    }

    input[type="range"] {
      width: 100%;
      accent-color: #8b5cf6;
      cursor: pointer;
      margin-bottom: 4px;
    }

    .range-val {
      font-size: 12px;
      color: #6b21a8;
      font-weight: 700;
      text-align: right;
    }

    .checkbox-row {
      display: flex;
      align-items: center;
      gap: 8px;
      margin-top: 6px;
    }
    .checkbox-row input[type="checkbox"] {
      width: 16px;
      height: 16px;
      accent-color: #60a5fa;
      cursor: pointer;
    }
    .checkbox-row label {
      margin-bottom: 0;
      cursor: pointer;
    }

    .btn-group {
      display: flex;
      flex-direction: column;
      gap: 8px;
    }
    .btn-group button {
      width: 100%;
      padding: 10px;
      border: none;
      border-radius: 6px;
      color: white;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
      transition: all .2s;
      box-shadow: 0 2px 4px rgba(0,0,0,.2);
    }
    .btn-group button:hover:not(:disabled) {
      transform: translateY(-1px);
      box-shadow: 0 4px 8px rgba(0,0,0,.25);
    }
    .btn-group button:disabled { opacity: .5; cursor: not-allowed; }

    #btn-reset   { background: #a78bfa; }
    #btn-reset:hover:not(:disabled)   { background: #8b5cf6; }
    #btn-shuffle { background: #06b6d4; }
    #btn-shuffle:hover:not(:disabled) { background: #0891b2; }
    #btn-solve   { background: #3b82f6; }
    #btn-solve:hover:not(:disabled)   { background: #2563eb; }

    /* ── stats ── */
    .stats {
      background: #ede9fe;
      border-radius: 8px;
      padding: 10px 12px;
      font-size: 12px;
      color: #6b21a8;
      line-height: 1.8;
    }
    .stats span { font-weight: 700; }

    /* ── visualizer ── */
    #visualizer {
      flex: 1;
      background: white;
      border: 3px solid #a78bfa;
      border-radius: 10px;
      box-shadow: 0 8px 16px rgba(0,0,0,.3);
      position: relative;
      overflow: hidden;
      min-height: 420px;
    }
    #visualizer canvas {
      position: absolute;
      inset: 0;
      width: 100%;
      height: 100%;
      display: block;
    }

    /* ── legend ── */
    .legend {
      display: flex;
      gap: 12px;
      flex-wrap: wrap;
      justify-content: center;
    }
    .legend-item {
      display: flex;
      align-items: flex-start;
      gap: 8px;
      background: rgba(0,0,0,.25);
      border-radius: 8px;
      padding: 8px 12px;
      min-width: 130px;
    }
    .dot {
      width: 12px; height: 12px;
      border-radius: 3px;
      flex-shrink: 0;
      margin-top: 2px;
    }
    .legend-text { display: flex; flex-direction: column; }
    .legend-label {
      font-size: 12px;
      font-weight: 700;
      color: rgba(255,255,255,.95);
      line-height: 1.3;
    }
    .legend-desc {
      font-size: 11px;
      color: rgba(255,255,255,.6);
      line-height: 1.3;
      margin-top: 1px;
    }
    .dot-default   { background: #8b5cf6; }
    .dot-outer     { background: #f59e0b; }
    .dot-minimum   { background: #ef4444; }
    .dot-sorted    { background: #22c55e; }
    .dot-comparing { background: #60a5fa; }

    /* ── stepwise button states ── */
    #btn-prev { background: #6366f1; }
    #btn-prev:hover:not(:disabled) { background: #4f46e5; }
    #btn-next { background: #3b82f6; }
    #btn-next:hover:not(:disabled) { background: #2563eb; }