JSFiddle - React, Tailwind, and code Playground

HTML

<div id="make_larger">
<button type="button">Large</button> 
</div>
<div id="make_small">
<button type="button">Smaller</button> 
</div>
<div id="make_normal">
<button type="button">Normal</button> 
</div>
<style type="text/css">
    .selected{background:blue}
</style>

JavaScript

$('#make_larger').click(function() {
     $('#make_larger button').addClass('selected');
});