JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parentDiv" style="width:200px; height:200px; background-color:#ff0">
    
    <div id="childDiv" style="display:none; width:100px; height:100px; background-color:#000"></div>
    
</div>

JavaScript

$(document).ready(function() {
    $("#parentDiv").mouseover(function() {
       $("#childDiv").show();
    }); 
});