微信小程序web-view上覆盖原生组件，解决cover-view点击事件无法触发问题

<web-view bindmessage="__e" class="webview data-v-68ffe378 vue-ref" data-event-opts="{{[ [ 'message',[ [ 'message',['$event'] ] ] ] ]}}" data-ref="currentWebview" src="{{url}}">
  <navigator url="/modules/WebviewApp/view/center">
  <cover-view class="duiba-back-btn">
<cover-image src="/static/back-btn.png"></cover-image> 
      </cover-view></navigator> 
</web-view>

/*  */
.duiba-back-btn {
    position: fixed;
    z-index: 999999;
    top:20rpx;
    left:0;
    width:100rpx;
    height:50rpx;
  }