JSFiddle - React, Tailwind, and code Playground

HTML

<button>
CLICK ME!
</button>
<div class="x active">

</div>

<div class="y">

</div>

CSS

div {
  height: 100px;
  display: none;
}

.x {
    background: #ccc
}

.y {
  background: green
}

.active {
  display: block;
}

JavaScript

const button = document.querySelector('button')
const y = document.querySelector('.y')


button.onclick = () => {
	y.classList.toggle('active')
}