JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="fixed">
  This is fixed!
  </div>
  
  <div class="content">&nbsp;</div>
</div>

CSS

.container {
  height:400px; 
  width:400px; 
  overflow-y: scroll;
  border:1px solid black;
}

.fixed {
  height:20px;
  width:150px;
  border: 1px solid black;
  background: gray;
  position: fixed;
  top:20px;
  left:20px;
}

.content {
  height:1200px;
}