JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flip-card">
  <div id="myLoader" class="flip-card-inner">
    <div class="flip-card-front">
       I'm hiding stuff that's loading!
    </div>
    <div id="loadedStuff" class="flip-card-back">

    </div>
  </div>
</div>

CSS

.flip-card {
  background-color: transparent;
  width: 300px;
  height: 200px;
  border: 1px solid #f1f1f1;
  perspective: 1000px; 
}

.flip-card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  text-align: center;
  transition: transform 0.8s;
  transform-style: preserve-3d;
}

.flip-card-front, .flip-card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  -webkit-backface-visibility: hidden; /* Safari */
  backface-visibility: hidden;
}

.flip-card-front {
  background-color: #bbb;
  color: black;
}

.flip-card-back {
  background-color: dodgerblue;
  color: white;
  transform: rotateY(180deg);
}

JavaScript

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
  if (xmlhttp.readyState == XMLHttpRequest.DONE) {
    if (xmlhttp.status == 200) {
      document.getElementById("loadedStuff").innerHTML = xmlhttp.responseText;
      animatedCardRotation(document.getElementById("myLoader"), 0, 180);
    }
  }
};

xmlhttp.open("GET", "https://www.httpbin.org/get", true);
xmlhttp.send();

function animatedCardRotation (Element, startDegree, endDegree) {
  if(startDegree < endDegree ) {
    startDegree += 10;
    Element.style.transform = `rotateY(${startDegree}deg)`;
    requestAnimationFrame( () => this.animatedCardRotation(Element, startDegree, endDegree) );
  }
}