JSFiddle - React, Tailwind, and code Playground

HTML

<div class="banner">
  <div class="text">
  ONLY NOW!
  </div>
</div>

CSS

.banner {
  background: #f00;
  height: 100px;
  width: 100px;
}

.text {
  font-size: 10vw;
}

JavaScript

let text = document.querySelector(".text");
setInterval(function() {
  let style = window.getComputedStyle(text, null).getPropertyValue('font-size');
  let fontSize = parseFloat(style); 
	console.log(fontSize + "px");
}, 1000);