<!DOCTYPE html> <!-- Any copyright is dedicated to the Public Domain. - http://creativecommons.org/publicdomain/zero/1.0/ --> <html> <style> summary { display: inline; /* ::first-line appiles only to inline element. */ } details::first-line { color: blue; } </style> <body> <details open> <summary>Summary <!-- Need ib-split so that the summary has multiple frames. --> <div>Block in summary</div> </summary> <span>This is the details.</span> </details> </body> </html>