JSFiddle - React, Tailwind, and code Playground

HTML

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<!--
Created using JS Bin
http://jsbin.com

Copyright (c) 2019 by dvoytenko (http://jsbin.com/qinarik/9/edit)

Released under the MIT license: http://jsbin.mit-license.org
-->
<meta name="robots" content="noindex">
<meta name="viewport" content="width=device-width,minimum-scale=1,initial-scale=1">
<title>Page 1</title>
<style>
body {
  margin: 0;
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  overflow: hidden;
}

[c] {
  margin: 8px;
  padding: 16px 8px;
  background: lightgray;
}

#fixed1 {
  position: fixed;
  ali
  left: 0;
  height: 25px;
  width: 100%;
  background: var(--bg, blue);
}
</style>
</head>
<body>

  Text 1
  Text 2

  <div id="fixed1">Fixed Header</div>  

  <div c>Div 1</div>
  <div c>Div 2</div>

  Text 3

  <div c>Div 3</div>

<script>
  for (var i = 4; i < 50; i++) {
    var e = document.createElement('div');
    e.setAttribute('c', '');
    e.textContent = 'Div ' + i;
    document.body.appendChild(e);
  }

  var sd = document.body.attachShadow({mode: 'open'});

  // Main slot will absorb all undistributed children.
  var mainSlot = document.createElement('slot');
  var scroller = document.createElement('div');
  scroller.style = 'background: lightblue; position: absolute; top: 0; left: 0;' +
      ' right: 0; bottom: 0;' +
      ' overflow-x: hidden; overflow-y: auto; -webkit-overflow-scrolling: touch;';
  scroller.appendChild(mainSlot);
  sd.appendChild(scroller);

  // Selectively, it's also possible to distribute fixed elements separately,
  // emulating fixed layer transfer.
  var fixedLayer = document.createElement('div');
  fixedLayer.style = 'height: 0; width: 0; position: fixed; overflow: visible;';
  fixedLayer.style.setProperty('--bg', 'green');
  sd.appendChild(fixedLayer);

  var mainFixedSlot = document.createElement('slot');
  mainFixedSlot.setAttribute('name', 'fixed');
  fixedLayer.appendChild(mainFixedSlot);
  
  function addToFixedLayer(element) {
 ...