JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div">привет</div>
<p id="poka">пока</p>

CSS

#poka {display:none;
transition:display 2s;

}

JavaScript

var div = document.getElementById('div');

var poka = document.getElementById('poka');

div.onmouseover = function() {
 poka.style.display='block'
}