JSFiddle - React, Tailwind, and code Playground

HTML

<div id="miElemento">
  <p></p>
</div>

CSS

#miElemento {
  border: solid 1px black;
  height: 100px;
  width: 100px;
}

#miElemento p:after{
  content:'Hello World';
}

JavaScript

var $elem = $("#miElemento  p")
var content = getComputedStyle($elem[0], ':after').content
console.log(content)