<!doctype html> <title>CSS Test Reference</title> <link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io"> <link rel="author" title="Mozilla" href="https://mozilla.org"> <style> #outer { width: 100px; height: 100px; } #inner { width: 100%; height: 100%; background: green; border-radius: 99px; } </style> <p>Should be a green circle below</p> <div id="outer"> <div id="inner"></div> </div>