JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main" ></div>

CSS

#main {
  width: 200px;
  height: 100px;
  border: 1px solid black
}

.first {
  background: blue;
}

.second {
  background: red;
}

JavaScript

let el = document.getElementById("main");

let timer = setInterval(function(){
	innerTimer = setTimeout(function(){
  	el.className = "first";
  }, 2000)
	el.className = "second";
}, 4000);