Detailed explanation of the content attribute in 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 attribute that can 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 embedded characters such as brackets, single quotes, and double quotes on both sides of the string. Set of text symbols. 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 href="http:///www.ido321.com">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)&#39;.&#39;;
}
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 content (counter name, numbering type) format syntax to specify the numbering type. The reference to 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 The numbers are nested within the medium numbers, and the small numbers are nested within the 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)&#39;.&#39;;
}
h1{
    counter-increment:h;
}
p::before{
    content:counter(p)&#39;.&#39;;
    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 result: https: //jsfiddle.net/dwqs/hfutu4Lq/

You can also achieve more complex nesting, such as three levels of 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)&#39;.&#39;;
}
h1{
    counter-increment:h1;
    counter-reset:h2;
}
h2::before{
    content:counter(h1) &#39;-&#39; counter(h2);
}
h2{
    counter-increment:h2;
    counter-reset:h3;
    margin-left:40px;
}
h3::before{
    content:counter(h1) &#39;-&#39; counter(h2) &#39;-&#39; counter(h3);
}
h3{
    counter-increment:h3;
    margin-left:80px;
}

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

Zhang Dada has an article about using counter to implement counting: small tip: CSS counter + pseudo class to achieve numerical dynamics Calculation and presentation

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