before和after，前者是在元素之前插入东西，后者是在元素后面插入东西，但插入的东西不仅仅只是文字而已，还有图标，以及计算器的操作。
由于两者的操作基本一样，这里以before为例
插入文字
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
p:nth-child(1)::before{
content: '插入文字'
}
p:nth-child(2)::before{
content: '插入❤'
}
p:nth-child(3)::before{
/*改变插入文字的颜色和背景*/
content: '插入文字';
background: skyblue;
color: #fff;
}
</style>
</head>
<body>
<p>段落1</p>
<p>段落2</p>
<p>段落3</p>
</body>
</html>
插入图片
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
p::before{
content: url('./菜单.svg'); /*图片地址*/
}
</style>
</head>
<body>
<p>段落1</p>
</body>
</html>
计数器
纯数字
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
/*
这里的add，可以是任意变量，但标签的counter-increment属性值要和上面的一样。
*/
h2::before{
content: counter(add);
}
h2{
counter-increment: add;
}
</style>
</head>
<body>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
</body>
</html>
拼接文本
计数器也可以拼接文本，不过不用什么加号之类
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before{
content: '第'counter(add)'章';
}
h2{
counter-increment: add;
}
</style>
</head>
<body>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
</body>
</html>
指定项目编号
content: counter(计数器名, 编号种类)
upper-alpha 大写字母
upper-roman 大写罗马字母
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before{
content: counter(add, upper-roman)'. ';
}
h2{
counter-increment: add;
}
</style>
</head>
<body>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
<h2>标题</h2>
</body>
</html>
编号嵌套
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before{
content: counter(add)'. ';
}
h2{
counter-increment: add;
counter-reset: addd; /*让子标题重新编号*/
}
h3::before{
content: counter(addd)'. ';
}
h3{
counter-increment: addd;
}
</style>
</head>
<body>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
</body>
</html>
在编号与编号加横线
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before{
content: counter(add)'. ';
}
h2{
counter-increment: add;
counter-reset: addd; /*让子标题重新编号*/
}
h3::before{
content: counter(add) '-' counter(addd)'. ';
}
h3{
counter-increment: addd;
padding-left: 40px;
}
</style>
</head>
<body>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h2>标题</h2>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
<h3>子标题</h3>
</body>
</html>
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before{
content: counter(add)'. ';
}
h2{
counter-increment: add;
counter-reset: addd; /*让子标题重新编号*/
}
h3::before{
content: counter(add) '-' counter(addd)'. ';
}
h3{
counter-increment: addd;
counter-reset: adddd;
padding-left: 40px;
}
h4::before{
content: counter(add) '-' counter(addd) '-' counter(adddd) '. ';
}
h4{
counter-increment: adddd;
padding-left: 40px;
}
</style>
</head>
<body>
<h2>标题</h2>
<h3>子标题</h3>
<h4>子标题的子标题</h4>
<h4>子标题的子标题</h4>
<h2>标题</h2>
<h3>子标题</h3>
<h4>子标题的子标题</h4>
<h4>子标题的子标题</h4>
<h2>标题</h2>
<h3>子标题</h3>
<h4>子标题的子标题</h4>
<h4>子标题的子标题</h4>
<h2>标题</h2>
<h3>子标题</h3>
<h4>子标题的子标题</h4>
<h4>子标题的子标题</h4>
</body>
</html>
在字符串两边添加嵌套文字符号
首先content有两个属性值，open-quote和close-quote，可以在文字两边添加如括号，单引号，双引号之类的文字符号。
open-quote是开始的符号，close-quote是结束符号，元素的样子中使用quotes属性来决定要什么符号。
不使用quotes属性时，默认是使用双引号
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before{
content: open-quote;
}
h2::after{
content: close-quote;
}
</style>
</head>
<body>
<h2>标题2</h2>
</body>
</html>
使用别的符号
<!doctype html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
<style type="text/css">
h2::before, h3::before{
content: open-quote;
}
h2::after, h3::after{
content: close-quote;
}
h2{
quotes: "("")"
}
h3{
/*转义字符*/
quotes: "\""\"
}
</style>
</head>
<body>
<h2>标题2</h2>
<h3>标题3</h3>
</body>
</html>