<cover-view class="square"></cover-view>
  .square{
    position: absolute;
    bottom: -18rpx;
    left: 41.5%;
    z-index: 9999;
    border: 18rpx solid ;
    border-top-color:   #003BAE;
    border-bottom-color: transparent;
    border-left-color: transparent;
    border-right-color: transparent;
  }