Как анимировать Div при прокрутке

var btn = document.querySelector('.button');
var btnUp = document.querySelector('.button-up')

btnUp.addEventListener('click', function() {
  document.querySelector(".parent").style.webkitTransform = "rotate(-90deg)";
  document.querySelector(".child").style.webkitTransform = "rotate(90deg)";
});

btn.addEventListener('click', function() {
  document.querySelector(".parent").style.webkitTransform = "rotate(0deg)";
  document.querySelector(".child").style.webkitTransform = "rotate(0deg)";
});

.parent {
  position: relative;
  width: 300px;
  height: 300px;
  border-radius: 50%;
  transform: rotate(-0deg);
  transition: transform 0.7s linear;
  margin: 100px auto 30px auto;
}

.child {
  position: absolute;
  transform: rotate(-0deg);
  transition: transform 0.7s linear;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  text-align: center;
  top: 278px;
  /* -child size/2 */
  left: 130px;
  /* parent size/2 - child size/2 */
}

<div class = "parent">
  <div class = "child">
    Data
  </div>
</div>

<button class = "button">Click Down</button>
<button class = "button-up">Click Up</button>