gallery-generator: Previous image button not working in web browsers based on Blink and WebKit

[win8linux]

Summary

When using a gallery, the previous image button does not work. Additionally the next image button will stop working correctly at the last image, instead functioning as a previous image button then as a next image button again.

Details

Issue can be replicated in these web browsers:

• Chromium 137.0.7151.119
• GNOME Web 48.3

Issue cannot be replicated in these web browsers:

• Firefox 140.0
• Falkon 25.04.2 (QtWebEngine 6.9.0)

[YellowAfterlife]

I am seeing this with Chromium 138 on Windows but I do not understand why - the way this works is like so:

• "Next page" is a <summary> element in a <details> element
• When it's clicked, an invisible element pushes it under the "Previous page" button
• Thus clicking "Previous page" collapses the <summary> with the next page and moves it back where it was

And now it doesn't do that in Chromium anymore - the invisible element overflows onto the next line even though they both are display: inline-block in a right-aligned <div> that's big enough for both of them.

[win8linux]

Testing with older versions of Chrome/Chromium on Windows, the gallery starts breaking at version 131.0.6778.109-r1368529 with the last known working version being 130.0.6723.92-r1356013.

Update:
Going through the Chrome 131 release notes, this may have been the cause of the breakage:
https://developer.chrome.com/blog/styling-details

[win8linux]

As of Firefox 143, this is now broken there too. I am currently working on my own CSS-only gallery carousel based on this implementation which with some changes can work similarly:

Screencast_20251013_204920.webm

Maybe the generator could be rebased on the same implementation too?