JSFiddle - React, Tailwind, and code Playground

HTML

<div id="box"></div>

CSS

#box {
    width:200px;
    height:200px;
    background-color:blue;
    opacity:0.5;
}

.fullColor {
    opacity:1.0;
}

JavaScript

$(document).ready(function() {
    $('div').click(function() {
        $(this).addClass('fullColor');
    });
});