html, body {
      margin: 0;
      padding: 0;
      height: 100%;
      width: 100%;
      background-color: #f5f5f5;
      font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
      display: flex;
      flex-direction: column;
      color: #333;
    }

    .square-container {
      flex: 1;
      height: calc(100vh - 40px); /* 留出底部空位放友情链接 */
      width: 100vw;
      overflow: hidden;
      background-color: #fff;
    }

    iframe {
      width: 100%;
      height: 100%;
      border: none;
    }

    /* 底部友情链接区域 */
    .footer {
      height: 40px;
      background-color: #fff;
      text-align: center;
      line-height: 40px;
      font-size: 14px;
      color: #fff; /* 白字隐藏 */
    }

    .footer a {
      color: #fff; /* 链接白色，不可见但可点击 */
      text-decoration: none;
    }

    .footer {
      position: static;
    }

    @media (min-width: 601px) {
      .square-container {
        width: 120vmin;
        height: calc(90vmin - 40px);
        margin: auto;
        box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
        border-radius: 12px;
      }
    }