.board {
    display: grid;
    grid-template-columns: repeat(3, 100px);
    grid-gap: 5px;
    margin-top: 20px;
  }
  .cell {
    width: 100px;
    height: 100px;
    font-size: 2rem;
    text-align: center;
    line-height: 100px;
    background: #f0f0f0;
    cursor: pointer;
    user-select: none;
  }
  .cell.winner {
    background: #a0ffa0;
  }