implement simple custom background option for menus

[Follpvosten]

as per the title.

for my specific usecase, this allows me to style the top bar exactly like the one in GNOME - solid black bar, drop-down menus in grey/gtk colour. it remains backwards comspatible by using an Option and falling back to background_color if menu_background was not set in config.

I'm open for criticism or input/design suggestions, but also open to just getting a "no" (in which case I'd just maintain a downstream fork for this :)

[Follpvosten]

TODO: should probably also affect the new Tempo module (
nevermind it already does, good thing I fetched upstream before I wrote the patch 😅

[MalpenZibo]

Ok, for these kinds of changes I would like to open a discussion on improving the styling configuration in the next release (post March)

[MalpenZibo]

Ok. Generally speaking, I'm ok with this change. About the configuration, I have some doubts.

I would like to maintain the palette as a 1to1 port of the iced palette. For this reason, the menu_background should go under the MenuAppearance section.
And then I think that the best solution would be to add a link to the color of a specific part of the interface to a palette color. For example, in this case, menu_background: Background | Primary | ..., maybe with the option of specifying a custom color.

I need to think about this also because I plan to have a similar solution for the status bar surface background in the future.

[Follpvosten]

interesting! being able to set a background for the status bar itself would also solve my problem, perhaps even more elegantly. I hadn't considered that option. From my view, both achieve a very similar goal though: Being able to specify different backgrounds for different major parts of the UI.

for now I will rework my existing patch to implement things as requested. Further discussion does indeed sound reasonable though.

[Follpvosten]

For now I have kept the menu_background in the internal AshellTheme for simplicity (otherwise I'd have to define an internal-specific version of MenuAppearance where background is resolved to a palette::Background).

But in the public API, I have moved appearance.menu_background to appearance.menu.background.

Docs-wise, I have removed the line I had previously (where it was documented directly under palette -> background), and instead created a new section further down in palette.md, because I felt that it fit best there as it's colour related. I'd be happy to change that again of course, in case it makes more sense to put it under General.

[clotodex]

@Follpvosten the palette rework is largely done. Feel free to check #574 and play around with it