style.css

.game-board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
    margin: 0 auto;
    width: 320px;
    height: 320px;
    border: 4px solid #666;
    border-radius: 10px;
    box-sizing: border-box;
  }
  
  .square {
    font-size: 90px;
    font-weight: bold;
    text-align: center;
    width: calc((320px - 2 * 4px - 2 * 10px) / 3);
    height: calc((320px - 2 * 4px - 2 * 10px) / 3);
    border-radius: 10px;
    border: 4px solid #666;
    cursor: pointer;
    transition: background-color 0.3s ease-in-out;
    box-sizing: border-box;
  }
  
  .square:hover {
    background-color: #ddd;
  }
  
  .square.marked-x {
    color: #ff6666;
  }
  
  .square.marked-o {
    color: #6666ff;
  }
  
  #game-message {
    margin-top: 20px;
    text-align: center;
    font-size: 20px;
    font-weight: bold;
  }

  .game-buttons {
    margin-top: 20px;
    text-align: center;
  }

  .game-buttons button {
    margin-right: 10px;
    border-radius: 5px;
    padding: 10px 20px;
    font-size: 16px;
    cursor: pointer;
    background-color: #eee;
    border: 2px solid #999;
  }

  .game-buttons button:hover {
    background-color: #ddd;
  }
  
  .game-buttons button:active {
    background-color: #ccc;
  }