JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="a">First</li>
    <li class="a">Second</li>
    <li class="a">Third</li>    
    <li class="b">First</li>
    <li class="b">Second</li>
    <li class="b">Third</li>    
    <li class="c">First</li>
    <li class="c">Second</li>
    <li class="c">Third</li>        
</ul>

CSS

ul li:nth-child(3n+3) {
    color: red;
}