JSFiddle - React, Tailwind, and code Playground

HTML

<body>

<div id="header">
header
</div>

<div id="main">
<pre id="someText"></pre>
</div>

</body>

CSS

html, body {
  margin: 0;
  padding: 0;
  overflow-y: hidden;
}

#header {
  position: fixed;
  background-color: teal;
  z-index: 1;
  top: 0;
  height: 100px;
  width: 100%;
}

#main {
  position: absolute;
  top: 100px;
  max-height: 100%;
  width: 100%;
  overflow-y: scroll;
}

JavaScript

document.getElementById("someText").innerText = "this is some content ".replace(/ /g, '\n').repeat(15);