JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box">

</div>

CSS

.box {
  width:100px;
  height:100px;
  background-color:black;
}
.red {
  background-color:red;
}

JavaScript

document.querySelector(".box").addEventListener("click", function(e) {
	e.target.classList.add(".red");
})