JSFiddle - React, Tailwind, and code Playground

HTML

<div class="intro_wrapper">
    <div id="slider"></div>
</div>

<div class="intro_wrapper">
</div>

CSS

.padded_intro_wrapper { padding: 20px; }
.intro_wrapper { background: #000; height: 100px; margin: 0 0 40px 0; width: 100px; }

JavaScript

// either of the below works

//$("#slider:parent").addClass('padded_intro_wrapper');

$('#slider').closest('.intro_wrapper').addClass('padded_intro_wrapper');