<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style type="text/css">
ul{
width: 200px;
margin: 0 auto;
}
ul li{
width: 200px;
height: 50px;
line-height: 50px;
text-align: center;
}
ul li::after{
content: ""; //注意这种用法
display: block; //before和after伪元素默认是行级元素
border-bottom: 1px solid red;
}
</style>
</head>
<body>
<ul>
<li>我要自学网1</li>
<li>我要自学网2</li>
<li>我要自学网3</li>
<li>我要自学网4</li>
<li>我要自学网5</li>
</ul>
</body>
</html>
原文：https://www.cnblogs.com/nanfengnan/p/14299811.html