有下面一段html代码：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
.triangle_up
{
height:0px; width:0px;
border-bottom:50px solid red;
border-left:50px solid transparent ;
border-right:50px solid transparent ;
}
</style>
</head>
<body>
<div class="triangle_up"></div>
</body>
</html><!DOCTYPE html>
<html lang="e
