JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
        <li>Hello</li>
</ul>

CSS

li:nth-child(2n):not(:nth-child(3n)) {
    background-color: green;
    color: white;
}