<style>
.up{
width:0;
height:0;
border: 100px solid transparent;
border-top: 100px solid red;/*红色*/
}
.down{
width:0;
height:0;
border: 100px solid transparent;
border-bottom: 100px solid blue;/*蓝色*/
}
.left{
width:0;
height:0;
border: 100px solid transparent;
border-left: 100px solid pink;/*黑色*/
}
.right{
width:0;
height:0;
border: 100px solid transparent;
border-right: 100px solid pink;/*黄色*/
}
</style>
<body>
<div class="up"></div>
<div class="down"></div>
<div class="left"></div>
<div class="right"></div>
</body>
实现效果
