only-child只有一个子元素的css样式
only-of-type只有一个元素的css样式
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<html lang="en">
<head><meta charset="UTF-8"><title>Document</title><style type="text/css">.box1 p:only-child/*只有一个儿子的就样式化*/{color: blue;}.test1 h2:only-of-type/*意思是*/{color: red;}</style>
</head>
<body><div class="box1"><p>hello king</p></div><div class="box1"><p>hello king</p><p>hello king</p></div><div class="test1"><h2>55</h2></div>
</body>
</html>
