section {
    margin: 100px auto;
    height:500px;
    width: 500px;
    background: url(../pic/0.jpg) no-repeat center center;
    background-size: cover;
    position: relative;
    border: 1px solid blue;
  }
  .l,.r {
    height:100% ;
    width: 50%;
    background-color: rgb(0, 0, 0);
    position: absolute;
    transition: all .9s;
  }
  .l {
    left: 0;
    top: 0;
    border-right: 1px solid skyblue;
    transform-origin: left;
    
  }
  .r {
    right: 0;
    top: 0;
    border-left: 1px solid skyblue;
    transform-origin: right;
   
    
  }
 section:hover .l{
    
   transform: rotateY(-180deg);
  }
  section:hover .r{
   transform: rotateY(180deg);
  }