下面的例子在每个 <h1>元素前面插入一幅图片 - 在线编辑器

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    h1:before {
      content: url(smiley.gif);
    }
  </style>
</head>

<body>
  <h1>This is a heading</h1>
  <p>The :before pseudo-element inserts content before an element.</p>
  <h1>This is a heading</h1>
  <p><b>注意:</b>仅当 !DOCTYPE 已经声明 IE8 支持这个内容属性</p>
</body>
</html>
​x
 
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    h1:before {
      content: url(smiley.gif);
    }
  </style>
</head>
​
<body>
  <h1>This is a heading</h1>
  <p>The :before pseudo-element inserts content before an element.</p>
  <h1>This is a heading</h1>
  <p><b>注意:</b>仅当 !DOCTYPE 已经声明 IE8 支持这个内容属性</p>
</body>
</html>