用CSS3画一个三角形

<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