<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style type="text/css">
.box{
width: 0px;
height: 0px;
background-color: white;
/* border-bottom: 50px solid transparent;
border-left: 50px solid transparent;
border-right: 50px solid transparent; */
border: 50px solid transparent;
border-top: 50px solid blue;
}
</style>
</head>
<body>
<div class="box"></div>
</body>
</html>！回车
div.box 回车
style 回车。。。。