JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>aaa</li>
    <li>bbb</li>
    <li>ccc</li>
</ul>

CSS

li{
    border:solid 1px;
    list-style:none;
    color:white;
    padding:.5em;
}

li:nth-child(2n){
    clear:both;
    float:left;
    background:red;
}
li:nth-child(2n-1) { 
    clear:both;
    float:right;
    background:blue;
}