JSFiddle - React, Tailwind, and code Playground

HTML

<div><span>ELEMENT</span></div>

CSS

div { margin: 20px; }
    span:after { content: 'AFTER'; position: absolute; }

    span.c1 { background: yellow; }
    span.c2:after { background: yellow; }

JavaScript

span = document.querySelector('span');

    span.addEventListener('click', function (e) {
        if (e.clientX > span.offsetWidth + span.offsetLeft) {
            span.className = 'c2';
        } else {
            span.className = 'c1';
        }
    });