JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<body>
  <div class="flip-container" id="flipFrame">
    <div class="flipper">
      <div class="front">
        FRONT CONTENT
        <br>
        <button id="myBtn" onclick="flipFrame()">
          Start <b>here</b>
        </button>
      </div>
      <div class="back">
        BACK CONTENT
      </div>
    </div>
  </div>
</body>

CSS

/* entire container, keeps perspective */
.flip-container {
    perspective: 1000;
    transform-style: preserve-3d;
}
/*  UPDATED! flip the pane when hovered */
.flip-container.hover .back {
    -webkit-transform: rotateY(0deg);
    -moz-transform: rotateY(0deg);
    -ms-transform: rotateY(0deg);
    transform: rotateY(0deg);    
}
.flip-container.hover .front {
    -webkit-transform: rotateY(180deg);
    -moz-transform: rotateY(180deg);
    -ms-transform: rotateY(180deg);
    transform: rotateY(180deg);       
}

.flip-container, .front, .back {
    width: 320px;
    height: 480px;
}

/* flip speed goes here */
.flipper {
    transition: 0.6s;
    transform-style: preserve-3d;

    position: relative;
}

/* hide back of pane during swap */
.front, .back {
    backface-visibility: hidden;
    transition: 0.6s;
    transform-style: preserve-3d;

    position: absolute;
    top: 0;
    left: 0;
}

/*  UPDATED! front pane, placed above back */
.front {
    z-index: 2;
    -webkit-transform: rotateY(0deg);
    -moz-transform: rotateY(0deg);
    -ms-transform: rotateY(0deg);
    transform: rotateY(0deg);    
}

/* back, initially hidden pane */
.back {
    -webkit-transform: rotateY(180deg);
    -moz-transform: rotateY(180deg);
    -ms-transform: rotateY(180deg);
    transform: rotateY(180deg);  
}

JavaScript

document.getElementById("myBtn").addEventListener("click", function() {
  document.querySelector("#flipFrame").classList.toggle("hover")
});