A detailed introduction to the content attribute of CSS3

There are four main pseudo-elements in CSS: before/after/first-letter/first-line. In the before/after pseudo-element selector, there is a content Attributes can be used to insert content into the page.

Insert plain text

content: "Inserted article", or content:none does not insert content

#html
<h1 id="这是h">这是h1</h1>
<h2 id="这是h">这是h2</h2>
#css
h1::after{
    content:"h1后插入内容"
}
h2::after{
    content:none
}

Running results: https://jsfiddle.net/dwqs/ Lmm1r08x/

Embedded text symbols

You can use the open-quote attribute value and close-quote attribute value of the content attribute to add brackets, single quotes, etc. on both sides of the string Nested literal symbols like double quotes. open-quote is used to add the starting text symbol, and close-quote is used to add the ending text symbol. Modify the above css:

h1{
    quotes:"(" ")";  /*利用元素的quotes属性指定文字符号*/
}
h1::before{
    content:open-quote;
}
h1::after{
    content:close-quote;
}
h2{
    quotes:"\"" "\"";  /*添加双引号要转义*/
}
h2::before{
    content:open-quote;
}
h2::after{
    content:close-quote;
}

Running result: https://jsfiddle.net/dwqs/p8e3qvv4/

Insert image

The content attribute can also be placed directly in front of the element/ After inserting the picture

#html
<h3 id="这是h">这是h3</h3>
#css
h3::after{
    content:url(http://ido321.qiniudn.com/wp-content/themes/yusi1.0/img/new.gif)
}

Run result: https://jsfiddle.net/dwqs/c6qk6pkv/

Insert the attribute value of the element

The content attribute can directly use attr to obtain the element attribute and insert it into the corresponding position.

#html
<a>这是链接</a>
#css
a:after{
    content:attr(href);
}

Run results: https://jsfiddle.net/dwqs/m220nzan/

Insert item number

Use the counter attribute of content to append consecutive numbers to multiple items.

#html
<h1 id="大标题">大标题</h1>
<p>文字</p>
<h1 id="大标题">大标题</h1>
<p>文字</p>
<h1 id="大标题">大标题</h1>
<p>文字</p>
<h1 id="大标题">大标题</h1>
<p>文字</p>
#css
h1:before{
    content:counter(my)'.';
}
h1{
    counter-increment:my;
}

Running results: https://jsfiddle.net/dwqs/2ueLg3uj/

Project number modification

The default inserted project number is numeric, 1,2 ,3. . . Automatic increment, you can also add text and styles to the project number, still use the above html, css modification is as follows:

h1:before{
    content:'第'counter(my)'章';
    color:red;
    font-size:42px;
}
h1{
    counter-increment:my;
}

Running results: https://jsfiddle.net/dwqs/17hqznca/

Specify the numbering type

Use the syntax of content (counter name, numbering type) format to specify the numbering type. The reference of the numbering type can be based on the list-style-type attribute value of ul. Using the above html, the css is modified as follows:

h1:before{
    content:counter(my,upper-alpha);
    color:red;
    font-size:42px;
}
h1{
    counter-increment:my;
}

Running results: https://jsfiddle.net/dwqs/4nsrtxup/

Number nesting

Large number nesting Nest numbers, and small numbers are nested within medium numbers.

#html
<h1 id="大标题">大标题</h1>
<p>文字1</p>
<p>文字2</p>
<p>文字3</p>
<h1 id="大标题">大标题</h1>
<p>文字1</p>
<p>文字2</p>
<p>文字3</p>
<h1 id="大标题">大标题</h1>
<p>文字1</p>
<p>文字2</p>
<p>文字3</p>
#css
h1::before{
    content:counter(h)'.';
}
h1{
    counter-increment:h;
}
p::before{
    content:counter(p)'.';
    margin-left:40px;
}
p{
    counter-increment:p;
}

Running results: https://jsfiddle.net/dwqs/2k5qbz51/

It can be found in the output of the example that the numbers of p are consecutive. If you renumber the three p's after each h1, you can use the counter-reset attribute to reset it, and modify the css of the above h1:

h1{
    counter-increment:h;
    counter-reset:p;
}

. In this way, the numbering will be reset. Take a look at the results: https://jsfiddle.net/dwqs/hfutu4Lq/

More complex nesting can also be achieved, such as three-level nesting.

#html
<h1 id="大标题">大标题</h1>
<h2 id="中标题">中标题</h2>
<h3 id="小标题">小标题</h3>
<h3 id="小标题">小标题</h3>
<h2 id="中标题">中标题</h2>
<h3 id="小标题">小标题</h3>
<h3 id="小标题">小标题</h3>
<h1 id="大标题">大标题</h1>
<h2 id="中标题">中标题</h2>
<h3 id="小标题">小标题</h3>
<h3 id="小标题">小标题</h3>
<h2 id="中标题">中标题</h2>
<h3 id="小标题">小标题</h3>
<h3 id="小标题">小标题</h3>
#css
h1::before{
    content:counter(h1)'.';
}
h1{
    counter-increment:h1;
    counter-reset:h2;
}
h2::before{
    content:counter(h1) '-' counter(h2);
}
h2{
    counter-increment:h2;
    counter-reset:h3;
    margin-left:40px;
}
h3::before{
    content:counter(h1) '-' counter(h2) '-' counter(h3);
}
h3{
    counter-increment:h3;
    margin-left:80px;

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