JSFiddle - React, Tailwind, and code Playground

HTML

<div id='foo'>

CSS

#foo {
 width: 100px;
 height: 50px;
 background: red;   
}

#bar {
    width: 10px;
    height: 10px;
    background: blue;
}

JavaScript

$("#foo").live("mouseenter mouseleave", function(e) {
    if (e.type == "mouseenter") {
       $("#foo").append("<div id='bar'>");
    } else {
        $("#bar").remove();
    }
});