<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>利用before.after</title> <style> body, ul, li, p {margin:0; padding:0; font-family:Verdana, Geneva, sans-serif;} ul li {list-style:none;} img {border:0 none} .focus {background:rgba(250,250,250,0.25); width:174px; height:174px; border:1px dashed #666; position:absolute; left:0px; top:0px; display:none;} .focus:before {width:174px; height:134px; border-left:1px solid #fff; border-right:1px solid #fff; content:‘‘; position:absolute; left:-1px; top:20px;} .focus:after {width:134px; height:174px; border-top:1px solid #fff; border-bottom:1px solid #fff; content:‘‘; position:absolute; top:-1px; left:20px;} .content .focus {display:block;} </style> </head> <body> <div class="content"> <a href=""><img src="jiawin_1.jpg" /> <p class="focus"></p></a> </div> </body> </html>
http://www.jiawin.com/css-before-after
原文：http://www.cnblogs.com/hellman/p/4250819.html