JSFiddle - React, Tailwind, and code Playground

HTML

<article>
    <p>test</p>
</article>

CSS

.focus article {
    color: green;
}

JavaScript

var	bod     = document.getElementsByTagName('body')[0],
    article = document.getElementsByTagName('article')[0];

article.onMouseOver = function(){
    
    bod.classList.add('focus');
}

article.onMouseOut = function(){
    
    bod.classList.remove('focus');
}

window.onLoad = function(){
    
    bod.classList.remove('loading');
}