<!doctype html>
<html>
<head>
<meta charset="UTF-8">
<title>带三角缺口的边框</title>
<style>
.out {
display:block;
width:0;
height:0;
border-left:6px dashed transparent;
border-right:6px dashed transparent;
border-top:0;
border-bottom:7px solid #ccc;
position:relative;
top:-7px;
left:50%;
}
.inner {
position:absolute;
border-left:6px dashed transparent;
border-right:6px dashed transparent;
border-top:0;
border-bottom:7px solid #fff;
left:-6px;
top:2px;
}
div {
position:relative;
margin:0 auto;
width:80px;
height:100px;
border:1px solid #ccc;
border-radius:5px;
}
</style>
</head>
<body>
<div>
<span class="out">
<span class="inner"></span>
</span>
</div>
</body>
</html>原文：http://www.cnblogs.com/liuxiaotao/p/4115239.html