JSFiddle - React, Tailwind, and code Playground

HTML

<div class="item"><p>TEST TEST</p></div>
<div class="item"><p>TEST TEST</p></div>
<div class="item"><p>TEST TEST</p></div>
<div class="item"><p>TEST TEST</p></div>
<div class="item"><p>TEST TEST</p></div>
<div class="item"><p>TEST TEST</p></div>

CSS

.test {
    background: red;
}

JavaScript

$("div.item:eq(2)").addClass("test");