JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.2.2/jquery.min.js"></script>
<div id="container">
  <div class="container-scroller">
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>
  TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT<br>TEXT
  </div>
  <div id="child"></div>
</div>

CSS

html, body {
  height: 100%;
}

body {
  margin: 0;
  font-family: sans-serif;
}

#container {
  position: relative;
  width: 80%;
  height: 80%;
  background-color: lightgrey;
}

.container-scroller {
  height: 100%;
  overflow-y: scroll;
}

#child {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  margin: auto;
  width: 50px;
  background-color: lightcoral;
  height: 100%;
}