JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">
<div id="b">
</div>
</div>

CSS

#a {
  width: 10em;
  height: 10em;
  position: relative;
  background-color: red;
  overflow-x: visible;
  overflow-y: auto;
}
#b {
  width: 10em;
  height: 2em;
  position: absolute;
  background-color: blue;
  opacity: 0.5;
  left: 5em;
  top: 5em;
}