HTML+CSS画一个三角形（宽高为0，三边透明）
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>triangle</title>
<style>
.triangle {
width: 0;
height: 0;
border: 100px solid transparent;
border-left-color: #f00;
}
</style>
</head>
<body>
<div class="triangle"></div>
</body>
</html> 效果：
