<!DOCTYPE html>
<html>
<head>
<style>
p::before {
content: "阅读此内容 -";
background-color: yellow;
color: red;
font-weight: bold;
}
</style>
</head>
<body>
<h1>::before 演示</h1>
<p>我的名字是唐老鸭。</p>
<p>我住在鸭堡。</p>
</body>
</html>