JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
<title>Post-Load CSS Rendering Test</title>
</head>
<body>
<div id="page">
<div id="slot">
<div class="green"></div>
</div>
</div>
</body>
</html>

CSS

body {
  background-color: red;
  padding: 0px;
  margin: 0px;
}

#page {
  display: table;
  height: 100%;
  width: 100%;
}

#slot {
  display: table-row;
  height: 100%;
  width: 100%;
}

JavaScript

var head = document.getElementsByTagName('head')[0];
if(!head) { alert("Couldn't find head tag"); return; }
var style = document.createElement('style');
style.innerHTML = ".green { background: green; height: 100%; width: 100%; }";
head.appendChild(style);