代码
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
.demo{
float: left;
}
.item,.item-2{
width: 100px;
height: 100px;
text-align: center;
line-height: 100px;
border: 1px solid #ccc;
background: #f2f2f2;
}
.item:nth-of-type(3){
background: red;
}
.item-2:nth-child(3){
background: red;
}
</style>
</head>
<body>
<div class="demo">
<p class="item">我是 p 标签</p>
<div class="item">1</div>
<div class="item">2</div>
<div class="item">3</div>
<div class="item">4</div>
</div>
<div class="demo">
<p class="item-2">我是 p 标签</p>
<div class="item-2">1</div>
<div class="item-2">2</div>
<div class="item-2">3</div>
<div class="item-2">4</div>
</div>
</body>
</html>
运行结果