.tag,.tag4,.tag3,.tag2{
  width: 0;
  height: 0;
  border: 100rpx solid;
}
.tag{
  border-left-color: red;
  border-right-color: transparent;
  border-bottom-color:transparent;
  border-top-color: transparent;
}
.tag2{
  border-left-color: transparent;
  border-right-color: transparent;
  border-bottom-color:transparent;
  border-top-color: yellow;
}
.tag3{
  border-left-color: transparent;
  border-right-color: blue;
  border-bottom-color:transparent;
  border-top-color: transparent;
}
.tag4{
  border-left-color: transparent;
  border-right-color: transparent;
  border-bottom-color:teal;
  border-top-color: transparent;
}
.box{
  display: flex;
  align-items: center;
  justify-content: center;
}



<view class="box">
  <view class="tag"></view>
<view class="tag2"></view>
<view class="tag3"></view>
<view class="tag4"></view>
</view>