JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>1</li>
    <li>2*</li>
    <li>3</li>
    <li>4</li>
    <li>5*</li>
    <li>6</li>
    <li>7</li>
    <li>8*</li>
    <li>9</li>
    <li>10</li>
    <li>11*</li>
</ul>

CSS

/* ul li:nth-child(6n+4),
ul li:nth-child(6n+5),
ul li:nth-child(6n+6) {
    background:red;
} */

ul li:nth-child(3n+2) {
    background:red;
}