JSFiddle - React, Tailwind, and code Playground

HTML

<div>some text</div>
<span class="secondclass"></span>
<span class="secondclass"></span>

CSS

.secondclass {
    display:inline-block;
    width:50px;
    height:50px;
    margin:10px;
    border:1px solid;
    background-color:#aaa;
}

span.secondclass:nth-of-type(2n+1) {
    background-color:red;
}