Support for dark mode

[philip-peterson]

I went looking for information on dark mode. It seems like it is normally supported by GTK4 apps through libadwaita. The way to access this through Rust may be libadwaita's StyleManager::is_dark.

https://docs.rs/libadwaita/latest/libadwaita/struct.StyleManager.html#method.is_dark

[sdroege]

As this is a general GTK question not directly related to the bindings, you'll probably have more luck at https://discourse.gnome.org

[martinling]

See greatscottgadgets/packetry#166 for an example of doing this without libadwaita.