Vue realizes click flip effect

//html code test demo naming copied randomly <div class="Demo">
        <div class="Before" :class="isTop ? 'contain-Before' : ''" @click="handleBefore"></div>
        <div class="After" :class="isTop ? 'contain-After' : ''" @click="handleAfter" style="font-size:20px;color:black">This is the back content</div>
    </div>

//Define isTop:false in data

//Method handleBefore() in methods{
  if(!this.isTop){
         this.isTop = true
     }
 },
 handleAfter(){
     if(this.isTop){
         this.isTop = false
     }
 }

//css
.Demo{
    width: 375px;
    height: 300px;
    margin-top: 50px;
    /* margin-left: 500px; */
    position: relative;
    perspective: 800px;
    box-sizing: border-box;
    
    
}
.Before{
    width: 100px;
    height: 200px;
    position: absolute;
    top:0;
    left: 0;
    background-repeat: no-repeat;
    background-position: center center;
    backface-visibility: hidden;
    transition: 1.5s;
    background-image:url('../assets/images/chunfen4.jpg');
    border:1px solid yellow;
 
}
.After{
    width: 100px;
    height: 200px;
    position: absolute;
    top:0;
    left: 0;
    color: #fff;
    background-color:#fff;
    text-indent: 2em;
    transform: rotateY(-180deg);
    backface-visibility: hidden;
    transition: 1.5s;
    border:1px solid yellow;
}
.Demo .contain-Before{
    transform: rotateY(180deg);
}
.Demo .contain-After{
    transform: rotateY(0deg);
}