add support for dark mode on macOS

[Foss-4]

Currently window title bar and settings are in light mode only.

Would be great if Mixxx adapted the macOS system setting to follow user preferences for dark / light mode and when users are using dark mode support showing the window title bar and preferences in dark mode.

[Be (be.ing)]

I think we have to update the macOS SDK used in the build environment:
https://doc.qt.io/qt-5/macos.html#opting-out-of-macos-behavior-changes

So this is blocked on https://github.com/mixxxdj/mixxx/pull/1974

[ronso0 (ronso0)]

we may simply load a dark palette for the main menubar since -right now- all our skins are rather dark.
See my latest comments in https://mixxx.zulipchat.com/#narrow/stream/109171-development/topic/Getting.20rid.20of.20the.20menu.20bar/near/202829332

[Foss-4 (foss-4)]

Closing this, dark mode is now supported thanks to the outstanding work @Be put into the macOS build process. Thanks so much - it is highly appreciated.

[ronso0 (ronso0)]

Nice.
Only the tree icons are kinda useless, except the Colors (brush) icon.
Maybe we should remove the gradients and make them all monochrome? That would only affect themes with a pure black background, with any other OS theme it would be fine IMO.

[Foss-4 (foss-4)]

re-opening. due to issues which were introduced using newer versions of xcode this got reverted and is thus unfixed again.

[Foss-4 (foss-4)]

And back to fix committed since https://github.com/mixxxdj/mixxx/pull/4225 was merged. Preferences and title bar are also respecting dark mode now.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10044