JSFiddle - React, Tailwind, and code Playground

HTML

<a href="#">HELLO!</a>

CSS

body {
    -webkit-transition: background-color 2s;
       -moz-transition: background-color 2s;
         -o-transition: background-color 2s;
            transition: background-color 2s;
    background-color: white;
}
.red {
    background-color: red;
}

JavaScript

$b = $('body');
$('a').mouseover(function(){
  $b.toggleClass('red', true );
}).mouseout(function(){
  $b.toggleClass('red', false );
});