css挤带边框的三角

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
.triangle{
width:100px;
background:#fff;
padding:10px 20px;
color:#333;
border-radius:4px;
position:absolute;
top:30px;
left:30px;
border:1px solid #333;
}
.triangle span{
display:block;
width:0;
height:0;
border-width:10px;
border-style:solid;
border-color:#333 #333 transparent transparent;
position:absolute;
top:8px;
left:-20px;
}
.triangle em{
display:block;
width:0;
height:0;
border-width: 10px;
border-style:solid;
border-color:#fff #fff transparent transparent;
position:absolute;
top:-9px;
left:-8px;
}
</style>
</head>
<body>
<div class="triangle">
<span><em></em></span>纯CSS写带边框的三角形
</div>
</body>
</html>