JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li id="a">a</li>
    <li id="b">b</li>
    <li id="c">c</li>
</ul>

<div id="result"></div>

CSS

ul {
    counter-reset: step;
}

li:before {
    counter-increment: step;
    content: counter(step) '. ';
}

JavaScript

var qs = function(query) {return document.querySelector(query);};

qs('#result').innerHTML = window.getComputedStyle(qs('#c'), ':before').getPropertyValue('content');