ios端有底部悬浮，安卓端没有

wxml
<view class="duiba-container">
  <view>
    <web-view src="{{readurl}}">
      <cover-view class="duiba-back-btn" bindtap="handleBackTo">
        <cover-image src="./../../images/btns.jpg"></cover-image>
      </cover-view>
    </web-view>
  </view>
</view>
wcss
.duiba-back-btn {
  position: fixed;
  z-index: 999999;
  bottom:0rpx;
  left:0;
  width:100%;
  height:136rpx;
}
.duiba-back-btn cover-image{
  width:100%;
  height:136rpx;
}