JSFiddle - React, Tailwind, and code Playground

HTML

<div class="red-circle"></div>

<div class="blue-square"></div>

CSS

.red-circle {
    height: 200px;
    width: 200px;
    border-radius: 50%;
    background: red;
    position: absolute;
    bottom: 25px;
    right: 25px;
}

.blue-square {
    height: 50px;
    width: 50px;
    background: blue;
    position: absolute;
    bottom: 25px;
    left: 25px;
}

JavaScript

$('.red-circle').mouseenter(function() {
     $('.blue-square').fadeOut();
});

$('.red-circle').mouseleave(function() {
     $('.blue-square').fadeIn();
});