1.画三角形 注意:宽高给0px,其他三个边框颜色调为透明
<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>Document</title>
<style>
div {
width: 0;
height: 0;
border: 50px solid transparent;
border-top: 50px solid yellow;
}
</style>
</head>
<body>
<div></div>
</body>
</html>
运行图:

2.画圆 注意:宽和高一定要相等,然后边框给50%
<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>Document</title>
<style>
.father{
margin: 30px auto;
width: 300px;
height: 300px;
border-radius: 50%;
background-color: yellow;
}
</style>
</head>
<body>
<div class="father">
</div>
</body>
</html>
运行图:
