标题
1.box-sizing:border-box
2.border-left/right/top/bottom
3.透明的颜色(transparent)
如下图:
<style>
body{
position: relative;
width: 100%;
height: 900px;
}
div{
position:absolute;
top: 0;
left: 0;
width: 100px;
height: 30px;
//核心代码
box-sizing: border-box;
border-bottom:30px solid red;
border-left: 20px solid transparent;
border-right: 20px solid transparent;
}
}
</style>