JSFiddle - React, Tailwind, and code Playground

HTML

<p id='c1.c1'>If css works, this should be red!<br/>
If js works, it will be green after JS ran!</p>
<a href='#' id='activate'>Run JS!</a>

CSS

#c1.c1 { 
    background:black;
}

JavaScript

var ev;
ev = document.getElementById('activate');
ev.onclick = function(){
    var el;
    el = document.getElementById('c1.c1');
    el.style.background = 'black';
};