We can follow to simplify the rules.

Port of https://hg.mozilla.org/mozilla-central/rev/81ca2d28c253

In https://hg.mozilla.org/integration/autoland/rev/c9399923df7b is an additional CSS change I add directly in this patch.

I've set leave-open because there is a patch in bug 1509931 in review that needs also a port.

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/04cba7f604c1
Port bug 1509931: Simplify titlebar buttons CSS. r=aleca

Taking this and using it to restructure our toolbar/titlebar/toolbox structure to follow Firefox and inherit the correct GTK styling for X11 and Wayland.
Not an easy change, but definitely necessary to guarantee correct titlebar moving forward.

Bug 1745419 will probably needs also to be ported.

Since today's trunk (97.0a1) the window top corners are properly rounded with the default, can you confirm, Richard?
Nonetheless, our implementation is not on par with m-c as multiple problems arise when trying to apply the same styling to the space toolbar.
Also as soon as a different theme is used, the styling is broken.
One more thing is that when using a LWTheme at full screen with a very large screen the background image doesn't resize properly and it's stuck in the middle.

Hopefully, all these issues will be addressed with this porting.

(In reply to Alessandro Castellani [:aleca] from comment #8)

Since today's trunk (97.0a1) the window top corners are properly rounded with the default, can you confirm, Richard?

This is already since longer time

Nonetheless, our implementation is not on par with m-c as multiple problems arise when trying to apply the same styling to the space toolbar.
Also as soon as a different theme is used, the styling is broken.

Yes, this for what this bug is.

One more thing is that when using a LWTheme at full screen with a very large screen the background image doesn't resize properly and it's stuck in the middle.

That should be normally right aligned but can also depend on the theme. Which theme are you testing? This is a limitation of the LW-themes with a background image which isn't wide enough. We don't stretch the image nor do we repeat it to fill the background which could look weird with themes that use a logo that has to be on a special position.

Pushed a WIP on phab so I can easily pull and push from my other computers to test on Windows and macOS.
Styling is partially broken and the titlebar buttons (max, min, close) need to be updated, but now the various themes are drawn correctly and the GTK CSD is respected.

I'm focusing on the main messenger window for now, the compose, address book (maybe not since we're removing it), and other standalone windows will follow later on.

Patch is ready for review!

This changes the structure quite a bit, so please be sure to check that everything looks good with the various windows in various states.

There's an annoying limitation due to the fact that we have multiple toolbars and not a single one like in m-c.
This limitation causes the LW-Themes that add a background image to not being visible underneath those various toolbars.
I temporarily solved the issue by reapplying that image to those toolbars. it should be acceptable for now, but we can then remove it after bug 1737361, which should provide a way to use a single toolbar that dynamically changes buttons based on the currently visible tab.

Try run: https://treeherder.mozilla.org/jobs?repo=try-comm-central&revision=fcc30b6fbe4323feb69e1e3ff709a78d1a7d2134

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/34e4ad62458f
Rebuild the titlebar HTML structure.r=mkmelin,Paenglab