<!DOCTYPE html> <!-- Any copyright is dedicated to the Public Domain. - http://creativecommons.org/publicdomain/zero/1.0/ --> <html> <style> body { width: 400px; } div#float { float: left; width: 200px; height: 400px; background-color: lightgreen; } details { float: left; background-color: orange; } summary { background-color: green; /* Hide the triangle for comparing with div in reftest. */ list-style-type: none; } </style> <body> <details open> <summary>Summary</summary> <div id="float"></div> </details> </body> </html>