用纯css画个三角形

用纯css画个三角形以下是源代码：
<!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>
<title>用纯css画个三角形-柯乐义</title>
</head>
<body>
<style type="text/css">
.rightdirection
{
width:0;height:0;
line-height:0;
border-width:20px;
border-style:solid;
border-color:transparent transparent transparent #A9DBF6;
}
.bottomdirection
{
width:0;height:0;
line-height:0;
border-width:20px;
border-style:solid;
border-color: #A9DBF6 transparent transparent transparent;
}
.leftdirection
{
width:0;height:0;
line-height:0;
border-width:20px;
border-style:solid;
border-color: transparent #A9DBF6 transparent transparent;
}
.topdirection
{
width:0;height:0;
line-height:0;
border-width:20px;
border-style:solid;
border-color: transparent transparent #A9DBF6 transparent;
}
</style>
<div class="rightdirection"></div>
<p>
<div class="bottomdirection"></div>
<p>
<div class="leftdirection"></div>
<p>
<div class="topdirection"></div>
</body>
</html>
参考：http://keleyi.com/a/bjac/j9nnxrqd.htm