JSFiddle - React, Tailwind, and code Playground

HTML

<div id=menu>menu<br>menu<br>menu<br>menu<br></div>
<div id="parent">
    <div id=up>up</div>
    <div id=down>down</div>
</div>

CSS

div {border: 1px solid black;}
#menu {float: right; width: 5em}
#parent {overflow: hidden;}
#up {float: right;}
#down{clear: right; float: right;}