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>
<li>12</li>
</ul>

CSS

li { width: 500px; background-color:blue; }
.zebra { background-color: red; }

JavaScript

$('ul li:nth-child(4n+3)').addClass("zebra").text("Here");