I was just about to implement a <details> + <summary> element where the summary is only as wide as its content, but on its own line. I actually did not want to hide the ::marker, but (1) having the summary is only as wide as its content and (2) show the marker. This is not possible in Webkit (Safari 17) due to "inline list-item" not being supported: https://bugs.webkit.org/show_bug.cgi?id=224809 Having the display property of a <summary> element set to something else but "list-item" does not show the ::marker arrow in Firefox and Chromium, but Safari does. I assume that this is what is suppose to happen. Here is a pen: https://codepen.io/scheinercc/pen/jOdBrEq So either way I set display to any flow value Webkit renders differently from the other engines.
A band aid fix is pretty straightforward here: https://searchfox.org/wubkat/rev/17d1d747ad3bb45ca5d2f0c735778816a3cd701f/Source/WebCore/html/shadow/DetailsMarkerControl.cpp#64 can just check for the display value.
<rdar://problem/118433698>
The larger underlying difference here is covered by bug 157323.