:root {
    --bg: #0f1220;
    --card: #171a2b;
    --text: #e9ecff;
    --muted: #b9bfdc;
    --accent: #7c5cff;
    --danger: #ff4d6d;
    --cell: #202444;
    --cellHover: #2a2f57;
    --win: #2ee59d;
    --border: rgba(255, 255, 255, 0.12);
  }
  
  * { box-sizing: border-box; }
  
  body {
    margin: 0;
    font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
    background: radial-gradient(1200px 700px at 30% 10%, rgba(124,92,255,0.25), transparent 60%),
                radial-gradient(900px 600px at 70% 30%, rgba(46,229,157,0.18), transparent 55%),
                var(--bg);
    color: var(--text);
    min-height: 100vh;
    display: grid;
    place-items: center;
    padding: 24px;
  }
  
  .app {
    width: min(520px, 100%);
  }
  
  .header h1 {
    margin: 0 0 6px 0;
    letter-spacing: 0.5px;
  }
  
  .sub {
    margin: 0 0 18px 0;
    color: var(--muted);
  }
  
  .panel {
    background: rgba(23, 26, 43, 0.85);
    border: 1px solid var(--border);
    border-radius: 18px;
    padding: 18px;
    box-shadow: 0 18px 60px rgba(0,0,0,0.35);
  }
  
  .status {
    font-size: 1.05rem;
    padding: 10px 12px;
    border-radius: 12px;
    background: rgba(255,255,255,0.06);
    border: 1px solid var(--border);
    margin-bottom: 14px;
  }
  
  .board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
    margin-bottom: 14px;
  }
  
  .cell {
    aspect-ratio: 1 / 1;
    border-radius: 14px;
    border: 1px solid var(--border);
    background: var(--cell);
    color: var(--text);
    font-size: clamp(2.2rem, 8vw, 3rem);
    font-weight: 700;
    cursor: pointer;
    display: grid;
    place-items: center;
    transition: transform 120ms ease, background 120ms ease, border-color 120ms ease;
  }
  
  .cell:hover {
    background: var(--cellHover);
    transform: translateY(-1px);
  }
  
  .cell:disabled {
    cursor: not-allowed;
    opacity: 0.75;
    transform: none;
  }
  
  .cell:focus-visible {
    outline: 3px solid rgba(124,92,255,0.8);
    outline-offset: 2px;
  }
  
  .cell.win {
    border-color: rgba(46,229,157,0.9);
    box-shadow: 0 0 0 2px rgba(46,229,157,0.25);
  }
  
  .controls {
    display: flex;
    gap: 10px;
  }
  
  .btn {
    flex: 1;
    padding: 10px 12px;
    border-radius: 12px;
    border: 1px solid var(--border);
    background: rgba(124,92,255,0.18);
    color: var(--text);
    font-weight: 600;
    cursor: pointer;
    transition: background 120ms ease, transform 120ms ease;
  }
  
  .btn:hover {
    background: rgba(124,92,255,0.28);
    transform: translateY(-1px);
  }
  
  .btn-secondary {
    background: rgba(255,255,255,0.06);
  }
  
  .btn-secondary:hover {
    background: rgba(255,255,255,0.10);
  }
  
  .help {
    margin-top: 12px;
    color: var(--muted);
    font-size: 0.92rem;
    line-height: 1.35;
  }
  
  .footer {
    margin-top: 14px;
    color: var(--muted);
    text-align: center;
  }