<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
i{
0;
height:0;
display:block;
border-style:solid;
border-0 20px 20px 20px;
border-color: transparent transparent red
}
</style>
</head>
<body>
<i></i>
</body>
</html>
效果：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
i{
0;
height:0;
display:block;
border-style:solid;
border-20px 20px 0 20px;
border-color:red transparent transparent;
}
</style>
</head>
<body>
<i></i>
</body>
</html>
效果：
