微信浏览器，video标签始终悬浮在最上层

加上这些属性

<video style="object-fit:fill" 
webkit-playsinline="true"  
x-webkit-airplay="true" 
playsinline="true"
x5-video-player-type="h5"
x5-video-orientation="h5" 
x5-video-player-fullscreen="true"
preload="auto"
></video>