【前端面试必读】实现图片16：9

<div class="img_wap">
   <img src=""/>
 </div>
.img_wap{
    padding-bottom: 56%;
    width: 100%;
    position: relative;
  }

  .img_wap img{
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;  
  }