JSFiddle - React, Tailwind, and code Playground

HTML

<div class="one">Блок 1</div>

<div class="blue">Блок 2</div>

CSS

.red{
  background-color: red;
}
.one, .blue{
  padding: 10px;
  border: 1px solid;
}
.one{
  margin-bottom: 10px;
}

JavaScript

let one = document.querySelector('div');
let blue = document.querySelector('.blue');

one.onclick = function(){
	this.classList.toggle('red');
}
if (one.classList.contains('red') !== true){
	blue.classList.add('red');
}
else{
	blue.classList.remove('red');
}