<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>document</title>
<!-- reset.css文件内容参考：https://www.cnblogs.com/lanshanxiao/p/12663192.html -->
<link rel="stylesheet" href="./reset.css">
<style>
div{
width:0;
height:0;
border:20px solid transparent;
border-right-color: #000;
}
</style>
</head>
<body>
<div>
</div>
</body>
</html>
效果展示：
