代码：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>002实现淘宝下三角</title>
<style type="text/css">
div {
width: 0px;
height: 0px;
/* background-color: #FF0000; */
border: 50px solid black;
border-top-color: transparent;
border-right-color: transparent ;
border-bottom-color:transparent ;
}
</style>
</head>
<body>
<div></div>
</body>
</html>
运行结果：