你也可以在 ::before 和 ::after 两个伪元素中添加阴影效果 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    #boxshadow {
      position: relative;
      -moz-box-shadow: 1px 2px 4px rgba(0, 0, 0, 0.5);
      -webkit-box-shadow: 1px 2px 4px rgba(0, 0, 0, .5);
      box-shadow: 1px 2px 4px rgba(0, 0, 0, .5);
      padding: 10px;
      background: white;
    }
    /* Make the image fit the box */

    #boxshadow img {
      width: 100%;
      border: 1px solid #8a4419;
      border-style: inset;
    }

    #boxshadow::after {
      content: '';
      position: absolute;
      z-index: -1;
      /* hide shadow behind image */
      -webkit-box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);
      -moz-box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);
      box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);
      width: 70%;
      left: 15%;
      /* one half of the remaining 30% */
      height: 100px;
      bottom: 0;
    }
  </style>
</head>
<body>

  <div id="boxshadow">
    <img src="/examples/rock600x400.jpg" alt="Norway" width="600" height="400">
  </div>

</body>
</html>
        