<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
div{
margin-top:20px;
}
.san1{
width:0;
height:0;
border-left:50px solid transparent;
border-right:50px solid transparent;
border-bottom:100px solid red;
}
.san2{
width:0;
height:0;
border-left:50px solid transparent;
border-right:50px solid transparent;
border-top:100px solid red;
}
.san3{
width:0;
height:0;
border-top:50px solid transparent;
border-bottom:50px solid transparent;
border-right:100px solid red;
}
.san4{
width:0;
height:0;
border-top:50px solid transparent;
border-bottom:50px solid transparent;
border-left:100px solid red;
}
</style>
</head>
<body>
<div class="san1"></div>
<div class="san2"></div>
<div class="san3"></div>
<div class="san4"></div>
</body>
</html>结果展示：
