JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
    <div class="inner1"><ul><li>an item</li></ul></div>
    <div class="inner2"></div>
</div>

CSS

.outer {
    width: 100px;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
    position: absolute;
}

.inner1 ul li {
    float: left;
}

.inner2 {
    width: auto;
    overflow: scroll;
}