JSFiddle - React, Tailwind, and code Playground

HTML

<button id="open">OPEN</button>

<div id="box">
<p>Текст</p>
<span class="close">&times;</span>
</div>

CSS

#box {
  width:300px;
  height:200px;
  background:yellow;
  display:none;
  position:relative;
}
.close {
  position:absolute;
  top:10px;
  right:10px;
  cursor:pointer;
  font-size:30px;
}

JavaScript

var open = document.querySelector("#open");
var close = document.querySelector(".close");

open.onclick = () => box.style.display ='block';

close.onclick = () => box.style.display ='none';