<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>伪元素</title>
</head>
<body>
<q>一些引用</q>，他说，<q>比没有好。</q>
</body>
</html>
输出：
::before
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>伪元素</title>
<style>
q::before {
content: "<<";
color: lightblue;
}
</style>
</head>
<body>
<q>一些引用</q>，他说，<q>比没有好。</q>
</body>
</html>
::after
<style>
q::before {
content: "<<";
color: lightblue;
}
q::after {
content: ">>";
color: lightcoral;
}
</style>
