body { font-family: sans-serif; padding: 20px; background: #f5f5f5; }
    #board {
      display: grid;
      grid-template-columns: repeat(5, 64px);
      gap: 8px;
      margin-top: 20px;
    }
    .cell {
      width: 64px;
      height: 64px;
      background: white;
      border: 2px solid #ccc;
      border-radius: 10px;
      font-size: 28px;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      user-select: none;
    }
    .selected {
      border-color: orange;
      background: #fff3e0;
    }
    .box {
      background: #e3f2fd;
    }