JSFiddle - React, Tailwind, and code Playground

HTML

<div class="thing1" onclick="change_the_after_attribute(this)">I am a thing. Click me.</div>

CSS

.thing1 {
  background-color:#ffcc88;
  display: inline-block;
}

.thing1::after {
  content:"I am what comes ::after a thing :)";
  display: inline-block;
  background-color: #4455ff;
  padding:3px;
  border: 1px solid #000000;
}

.thing1.extra_stuff::after {
  content:"Some parts of me, changed!";
  background-color: #8888cc;
}

JavaScript

function change_the_after_attribute(thing_button) {
	thing_button.className="thing1 extra_stuff";
}