匹配属于父元素中第一个子元素的每个<p>元素 - 在线编辑器

          <!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <style>
    p:first-child {
      background-color: yellow;
    }
  </style>
</head>
<body>

  <p>This paragraph is the first child of its parent (body).</p>

  <h1>Welcome to My Homepage</h1>
  <p>This paragraph is not the first child of its parent.</p>

  <div>
    <p>This paragraph is the first child of its parent (div).</p>
    <p>This paragraph is not the first child of its parent.</p>
  </div>

  <p><b>注意:</b> :first-child作用于 IE8以及更早版本的浏览器, DOCTYPE必须已经声明.</p>

</body>
</html>
        