JSFiddle - React, Tailwind, and code Playground

HTML

<section>
  <div>
    Hello world
  </div>
</section>

CSS

section {
  border: 2px red dotted;
}

JavaScript

setTimeout(() => {
	const section = document.querySelector('section')
  var newElement = document.createElement('div');
	newElement.textContent = "new content";         
  section.appendChild(newElement)
}, 3 * 1000)