JSFiddle - React, Tailwind, and code Playground

HTML

<div>1</div>
<div>2</div>
<div>3</div>
<div>4</div>
<div>5</div>
<div>6</div>
<div>7</div>
<div>8</div>
<div>9</div>
<div>10</div>

CSS

div:nth-child(4n), div:nth-child(4n-1) {
    background: red;
}
div:nth-child(4n-2), div:nth-child(4n-3) {
    background: blue;
}