JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <ul id="first-menu">
        <li>item-1</li>
        <li>item-2</li>
    </ul>
</div>

<div>
    <ul id="second-menu">
        <li>item-1</li>
        <li>item-2</li>
        <li>item-3</li>
        <li>item-4</li>
        <li>item-5</li>
    </ul>
</div>

CSS

li {
    color: white;
}

ul li:nth-child(2n) {
    background-color: #AA5555;
}

ul li:nth-child(2n+1) {
    background-color: #5555AA;
}