设置一个div元素的透明度级别 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <style>
    div {
      background-color: red;
      opacity: 0.5;
      filter: Alpha(opacity=50);
      /* IE8 and earlier */
    }
  </style>
</head>
<body>

  <div>This element's opacity is 0.5! Note that both the text and the background-color are affected by the opacity level!</div>

</body>
</html>
        