<!DOCTYPE>
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style type="text/css" >
.index_nav a:hover i, .index_nav a.on i {
display: inline-block;
width: 0;
height: 0;
font-size: 0;
overflow: hidden;
position: absolute;
bottom: -26px;
left: 50%;
border: 13px dashed transparent;
border-top: 13px solid #ea331a;
}
</style>
</head>
<body>
<div class="index_nav clearfix">
<a href="javascript:;" class="on">12月17日<i></i></a>
</div>
</body>
</html>
效果截图：
原文：http://www.cnblogs.com/webfby/p/4174490.html