wxml：

    <!-- 小程序悬浮按钮进入内页 -->
    <navigator class="set_button" url='../set/set' hover-class='none'>
      <image class="set_image" src="/images/set.png"></image>
    </navigator>

wxss：

    .set_button{
      background-color: rgba(255, 255, 255, 0);
      border: 0px;
      height: 120rpx;
      right: 20rpx;
      bottom: 20rpx;
      position: fixed;
    }
    .set_button::after{
      border: 0px;
    }
    .set_image{
      width: 120rpx;
      height: 120rpx;
    }