1.先画一个正方形
2.在定义4条边框，你想那个三角形朝哪个方向就给那条边框定义颜色，其余边框颜色设置透明。
transparent ：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>如何绘制三角形</title>
<style>
.jiang{
height: 0px;
width: 0px;
/* background: green; */
border-bottom: 100px solid greenyellow;
border-top: 100px solid transparent;
border-left: 100px solid transparent;
border-right: 100px solid transparent;
}
</style>
</head>
<body>
<!-- 1。绘制大小的正方形 -->
<div class="jiang"></div>
</body>
</html>
