1 <!DOCTYPE html> 2 <html> 3 <head> 4 <meta charset="UTF-8"> 5 <title></title> 6 <style type="text/css"> 7 8 .ha{ 9 text-align: center; 10 width: 200px; 11 height: 200px; 12 background-color: green; 13 } 14 /*hover:鼠标悬停后有动态解释效果*/ 15 .ha:hover{ 16 width: 500px; 17 height: 500px; 18 background-color: yellowgreen; 19 } 20 21 /*after:在元素里面的尾部插入内容*/ 22 .ha:after{ 23 content: '!!!!'; 24 background-color: red; 25 } 26 27 /*before:在元素里面的头部插入内容*/ 28 .ha:before{ 29 content: '$$'; 30 color: darkblue; 31 } 32 </style> 33 </head> 34 <body> 35 <div class="ha" >伪类及伪元素选择器</div> 36 </body> 37 </html>