<html> <head> <title></title> <style type="text/css"> *{ padding: 0; margin: 0; } .box{ position: relative; width: 100px; height: 100px; background: #f00; } .box:after{ position: absolute; left: 0; bottom: 0; content: ‘‘; width: 0; height: 0; border-left: 50px solid transparent; border-right: 50px solid transparent; border-bottom: 10px solid #fff; } </style> </head> <body> <div class="box"></div> </body> </html>
原文：http://www.cnblogs.com/beast-king/p/5572707.html