html, body {
      height: 100%;
      margin: 0;
      background-color: #f8f9fa;
    }
    body {
      display: flex;
      justify-content: center;    /* 水平居中 */
      align-items: flex-start;    /* 顶部对齐 */
      padding-top: 30px;          /* 距离顶部30px */
      padding-left: 15px;
      padding-right: 15px;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
      min-height: 100vh;
      box-sizing: border-box;
    }
    .container {
      max-width: 480px;
      width: 100%;
      background: white;
      padding: 2rem;
      border-radius: 8px;
      box-shadow: 0 0 15px rgba(0,0,0,0.1);
      box-sizing: border-box;
    }
    /* 输入框淡淡背景色 */
    #shorten-form input.form-control {
      background-color: #f0f0f0;
      border-radius: 5px;
      border: 1px solid #ccc;
      padding: 10px 12px;
    }
    /* 按钮100%宽度 */
    #submit-btn {
      width: 100%;
      font-weight: 600;
      padding: 0.5rem 0;
    }
    .container {
    
  width: 100%;
  max-width: 480px; /* 手机默认最大宽度 */
  background: white;
  padding: 2rem;
  border-radius: 8px;
  box-shadow: 0 0 15px rgba(0,0,0,0.1);
  box-sizing: border-box;
  margin: 0 auto;
}

/* 大屏幕时加宽容器 */
@media (min-width: 992px) {
  .container {
    max-width: 720px;
  }
}