html, body {
    margin: 0;
    padding: 0;
    height: 100%;
    background: #333;  /* 背景色，可根据需求调整 */
    display: flex;
    align-items: center;
    justify-content: center;
  }
  
  .game-container {
    border: 2px solid #fff; /* 边界线 */
    box-shadow: 0 0 10px rgba(0,0,0,0.5);
  }