JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li class = "tab"><a href="#">One</a></li>
  <li class = "tab"><a href="#">Two</a></li>
  <li class = "tab active"><a href="#">Three</a></li>
  <li class = "tab"><a href="#">Four</a></li>
</ul>

CSS

li {
  width: 50px;
  background-color: grey;
  display: inline-block;
  text-align: center;
}

a {
  color: #fff;
  text-decoration: none;
}

.active {
  background-color: yellow;
}

JavaScript

var NumThree = document.querySelector("li.tab active")

function removeActiveClass(){
	if(NumThree !== null) {
		NumFour.classList.remove("active")
	}
}