<view class="span"></view>

span {
    position: absolute;
    width: 0;
    height: 0;
    left: 0px;
    width: 0;
    height: 0;
    border-right: 100px solid red;
    border-left: 100px solid green;
    border-top: 100px solid yellow;
    border-bottom: 100px solid blue;
    border-radius: 100%;
}