JSFiddle - React, Tailwind, and code Playground

HTML

<ol>
<li>stuff</li>
<li>stuff</li>
<li>stuff</li>
<li>stuff</li>
<li>stuff</li>
<li class="test_class">stuff</li>
<li>stuff</li>
<li>stuff</li>
<li>stuff</li>
</ol>

JavaScript

$(function(){
    $('li:nth-child(3n)').not('.test_class').css('color', 'red'); 
});