JSFiddle - React, Tailwind, and code Playground

by LuckyCat

HTML

<!DOCTYPE html>
<html style="font-size:26%">
<head></head>
<body>
   <div style="width:100rem; height:100rem; background:blue;"></div>
</body>
</html>

JavaScript

var width= document.querySelector('div')
  .getBoundingClientRect()
  .width;
  
var html = document.getElementsByTagName('html')[0];

var targetWidth = window.getComputedStyle(html)['font-size']
	.split('px')[0] * 100;

var difference = Math.abs(targetWidth - width);

var msg = 'Actual Width: ' + width +
	'\nTarget Width: ' + targetWidth +
	'\nDifference: ' + difference;
if (difference !== 0) {
	msg = 'FAIL!\n' + msg;
} else {
	msg = 'OK!\n' + msg;
}

alert(msg)