JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main">
    <a id="link" href="#">hover me to fade out main</a>   
</div>

CSS

#main {
    -webkit-transition: opacity 0.3s;
    -moz-transition: opacity 0.3s;
    -ms-transition: opacity 0.3s;
    -o-transition: opacity 0.3s;
    transition: opacity 0.3s;
    height:400px;
    width:400px;
    background:red
}

.hover {
    opacity: 0.3;
}

JavaScript

$('#link').hover(function(){
    $('#main').addClass('hover');
}, function(){
   $('#main').removeClass('hover');
})