What are the functions of :after and :before in CSS_html/css

What are the functions of :after and :before in CSS_html/css_WEB-ITnose

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Release： 2016-06-24 11:41:18

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What are the functions of :after and :before in CSS:
In the current page layout, the frequency of use of :after and :before pseudo-object selectors does not seem to be very high, because Lower versions of IE browsers do not support it, but they are also used in clear floats or any other related layouts. However, as the usage of lower version browsers declines, their frequency should increase accordingly. Let’s briefly introduce the usage of these two pseudo-object selectors. Let’s first look at a code example:

<!DOCTYPE html> <html> <head> <meta charset=" utf-8"> <meta name="author" content="http://www.51texiao.cn/" /> <title>蚂蚁部落</title> <style type="text/css"> div:before{   content:"添加的内容"; } </style> </head> <body> <div>|div原来的内容</div> </body> </html>

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The above code can add specified content to the internal front end of the div element. Of course: the before pseudo-object selector is implemented in conjunction with the content attribute.
Grammar structure:

E:before{ Rules }E::before{ Rules }

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E represents elements matched by selectors, for example:

div:before.first:before#mytest:before

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in the grammar You can see that there are two grammatical forms, one is with a ":" in front of before, and the other is with two ":" in front of before. The first is the CSS2 way of writing, and the second is the CSS3 way of writing. IE7 and browsers below IE7 do not support CSS2 writing, and browsers IE8 and below do not support CSS3 writing. The :before pseudo-object selector is generally used in conjunction with the content attribute to add specified content to the front end inside the specified matching element. The use of the :after pseudo-object selector is the same as the use of :before and will not be introduced.

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