JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>item1</li>
    <li>item2</li>
    <li>item3</li>
    <li>item4</li>
    <li>item5</li>
    <li>item6</li>
    <li>item7</li>
    <li>item8</li>
    <li>item9</li>
</ul>

CSS

ul {
    margin: 20px;
    width: 170px;
}

ul li {
    padding: 10px;
    float: left;
    border-bottom: 1px solid #aaa;
}

ul:after {
    clear: both;
    content: "";
    display: table;
}