1.需要哪个三角形就
<meta charset="UTF-8">
<title>Title</title>
<style>
div{
border: 20px solid;
border-color: black red yellow green;/*上右下左*/
height: 0;
width: 0;
}
</style>
</head>
<body>
<div></div>
</body>
</html>
原文：http://www.cnblogs.com/bravolove/p/6208733.html