:root {
    --bg: #0f172a;
    --panel: #1e293b;
    --text: #f1f5f9;
    --muted: #94a3b8;
    --frame: #1d4ed8;
    --frame-edge: #1e40af;
    --well: #0b1120;
    --red: #ef4444;
    --yel: #facc15;
    --accent: #60a5fa;
    /* The board is 7 columns × 7 rows: the top row is the open staging lane
       discs drop through, the bottom 6 are the framed grid. The vh term keeps
       it (plus header, name rows and controls) inside short/wide windows. */
    --board: min(94vmin, 560px, calc(100vh - 220px));
    --cell: calc(var(--board) / 7);
  }
  * { margin: 0; padding: 0; box-sizing: border-box; }
  html, body {
    height: 100%;
    overflow: hidden;
    background: var(--bg);
    color: var(--text);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    touch-action: manipulation;
    -webkit-user-select: none;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
    overscroll-behavior: none;
  }
  body {
    position: fixed;
    inset: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 10px;
    height: 100vh;
    height: 100dvh;
    padding: max(10px, env(safe-area-inset-top))
             max(10px, env(safe-area-inset-right))
             max(10px, env(safe-area-inset-bottom))
             max(10px, env(safe-area-inset-left));
  }
  header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: var(--board);
    gap: 10px;
  }
  header a { color: var(--muted); text-decoration: none; font-size: 14px; white-space: nowrap; }
  #status { font-size: 15px; font-weight: 600; text-align: right; min-height: 1.2em; }
  #wrap { position: relative; }
  #board { position: relative; width: var(--board); aspect-ratio: 1; }
  /* Layers, bottom to top: the dark well behind the holes, the discs (static +
     falling), the frame with punched-out holes the discs show through, and the
     column tap strips. A falling disc starts in the open lane above the frame,
     then passes behind it — visible only through the holes, like the real toy. */
  #well {
    position: absolute;
    left: 0; right: 0; bottom: 0;
    top: var(--cell);
    background: var(--well);
    border-radius: 12px;
  }
  #discs { position: absolute; inset: 0; z-index: 1; }
  #frame {
    position: absolute;
    left: 0; right: 0; bottom: 0;
    top: var(--cell);
    z-index: 2;
    pointer-events: none;
    border-radius: 12px;
    background: radial-gradient(circle closest-side, transparent 0 70%, rgba(0, 0, 0, 0.35) 71% 79%, var(--frame) 80%)
                0 0 / calc(100% / 7) calc(100% / 6);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.45), inset 0 0 0 2px var(--frame-edge);
  }
  #cols { position: absolute; inset: 0; z-index: 3; display: flex; }
  .colstrip { flex: 1; position: relative; cursor: pointer; }
  /* Ghost of your disc in the lane over the hovered column (desktop only) */
  .colstrip::before {
    content: "";
    position: absolute;
    top: calc(var(--cell) * 0.1);
    left: 10%;
    width: 80%;
    height: calc(var(--cell) * 0.8);
    border-radius: 50%;
    background: var(--you, transparent);
    opacity: 0;
    transition: opacity 0.1s;
  }
  @media (hover: hover) {
    #board:not(.busy) .colstrip:hover { background: rgba(255, 255, 255, 0.04); }
    #board:not(.busy) .colstrip:hover::before { opacity: 0.35; }
  }
  #board.busy .colstrip { cursor: default; }
  .cell {
    position: absolute;
    width: calc(100% / 7);
    height: calc(100% / 7);
    display: flex;
    align-items: center;
    justify-content: center;
  }
  .cell.fall {
    transition-property: transform;
    /* accelerate like gravity; duration is set per drop from the fall height */
    transition-timing-function: cubic-bezier(0.5, 0, 0.85, 0.6);
    will-change: transform;
  }
  .pc {
    width: 80%;
    height: 80%;
    border-radius: 50%;
    position: relative;
    box-shadow: 0 3px 6px rgba(0, 0, 0, 0.45), inset 0 -4px 0 rgba(0, 0, 0, 0.3), inset 0 3px 0 rgba(255, 255, 255, 0.18);
  }
  .pc.red { background: radial-gradient(circle at 35% 30%, #f87171, #b91c1c 70%); }
  .pc.yel { background: radial-gradient(circle at 35% 30%, #fde68a, #d97706 72%); }
  /* The freshest disc gets a marker dot and a little landing squash */
  .pc.last { animation: settle 0.16s ease-out; transform-origin: 50% 100%; }
  .pc.last::after {
    content: "";
    position: absolute;
    inset: 41%;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.65);
  }
  @keyframes settle { from { transform: scaleY(0.78); } to { transform: scaleY(1); } }
  .pc.winline { animation: winpulse 0.7s ease-in-out infinite alternate; }
  @keyframes winpulse { from { filter: brightness(1); } to { filter: brightness(1.7); } }
  /* The robot's hand: hovers in the lane holding its disc, then opens */
  .hand {
    position: absolute;
    top: 0;
    width: calc(100% / 7);
    height: calc(100% / 7);
    z-index: 4;
    display: flex;
    align-items: center;
    justify-content: center;
    pointer-events: none;
    opacity: 0;
    transform: translateY(-45%);
    will-change: left, transform, opacity;
  }
  .hand.in { opacity: 1; transform: translateY(0); }
  .hand.out { opacity: 0; transform: translateY(-55%); }
  .hand .mitt {
    position: absolute;
    left: 50%;
    top: -12%;
    transform: translateX(-50%) rotate(180deg); /* reaching down from above */
    font-size: calc(var(--cell) * 0.66);
    line-height: 1;
    filter: drop-shadow(0 3px 4px rgba(0, 0, 0, 0.5));
  }
  /* Player rows: just names here — Connect Four has no captures to count */
  .player { display: flex; flex-direction: column; gap: 3px; width: var(--board); }
  .player .name { display: flex; align-items: center; gap: 6px; font-size: 14px; font-weight: 700; min-height: 17px; }
  .player .name .sub { color: var(--muted); font-weight: 600; font-size: 12px; }
  .dot {
    width: 14px;
    height: 14px;
    border-radius: 50%;
    flex: 0 0 auto;
    box-shadow: inset 0 -2px 0 rgba(0, 0, 0, 0.3), inset 0 2px 0 rgba(255, 255, 255, 0.18);
  }
  .dot.red { background: radial-gradient(circle at 35% 30%, #f87171, #b91c1c 70%); }
  .dot.yel { background: radial-gradient(circle at 35% 30%, #fde68a, #d97706 72%); }
  #controls { display: flex; gap: 10px; width: var(--board); }
  /* Engine evaluation bar: the filled width is the player's share of the position */
  #eval {
    width: var(--board);
    height: 16px;
    border-radius: 8px;
    background: #242a3a;
    position: relative;
    overflow: hidden;
    box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.08);
  }
  #eval-fill {
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 50%;
    transition: width 0.25s ease;
  }
  #eval-score {
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 11px;
    font-weight: 800;
    color: #f1f5f9;
    text-shadow: 0 1px 3px rgba(0, 0, 0, 0.9);
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.03em;
  }
  button {
    flex: 1;
    padding: 12px;
    border: 2px solid rgba(255, 255, 255, 0.14);
    border-radius: 12px;
    background: var(--panel);
    color: var(--text);
    font: 700 15px -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    cursor: pointer;
    touch-action: manipulation;
  }
  button:active { background: #34405f; }
  button:disabled { opacity: 0.4; }
  .winbanner {
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    font-size: clamp(36px, 11vmin, 72px);
    font-weight: 800;
    color: #fbbf24;
    text-shadow: 0 3px 12px rgba(0, 0, 0, 0.7);
    z-index: 6;
    pointer-events: none;
    animation: pop 0.5s cubic-bezier(0.2, 2.2, 0.4, 1);
  }
  @keyframes pop { from { transform: scale(0.2); opacity: 0; } to { transform: scale(1); opacity: 1; } }
  #overlay {
    position: absolute;
    inset: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 16px;
    background: rgba(10, 12, 26, 0.88);
    -webkit-backdrop-filter: blur(5px);
    backdrop-filter: blur(5px);
    border-radius: 8px;
    padding: 20px;
    text-align: center;
    z-index: 5;
  }
  #overlay.hidden { display: none; }
  #overlay h1 { font-size: 30px; font-weight: 800; }
  #overlay .row { display: flex; gap: 10px; width: 100%; max-width: 320px; }
  #overlay .row button.on { border-color: var(--accent); background: #16283f; }
  #overlay label { color: var(--muted); font-size: 14px; }
  #overlay label.opt { display: flex; align-items: center; gap: 8px; cursor: pointer; }
  #overlay label.opt input { width: 18px; height: 18px; accent-color: var(--accent); cursor: pointer; }
  #overlay input[type=range] { width: 100%; max-width: 320px; }
  #lvl-label { font-size: 20px; font-weight: 800; color: var(--accent); }
  #ov-msg { color: var(--muted); font-size: 15px; line-height: 1.5; }