JSFiddle - React, Tailwind, and code Playground

HTML

<div class="list-group" id="setActive">
        <a href="#">aaa</a>
        <a href="#">bbb</a>
        <a href="#">ccc</a>
    </div>

CSS

.list-item {
        color: red;
    }

JavaScript

document.addEventListener('DOMContentLoaded', function() {
        var setActive = document.querySelector('#setActive'),
            anchors = setActive.querySelectorAll('a');
    
        [].forEach.call(anchors, function(anchor) {
            anchor.classList.add("list-item");
        });
    
    });