Support "dark mode"
With Qt 5.12, the dark mode in macOS 10.14+ should work fairly well. And now that we finally have a dark theme working in macOS, we should reinstate & fix the old dark theme support that used to exist in SV long ago! (It was dropped because it was incomplete & there was no way to make it work in OS/X)
- Linux desktop environments can usually be set to a dark theme, but Qt doesn't always seem to follow this. It might be nice if SV on Linux could be set to use a light/dark theme independent of the desktop settings. It would be nice(r) if it could actually follow the desktop theme consistently!
- Windows 10 has a light/dark toggle for "app mode" in the settings - this presumably only directly affects UWP-type apps, but I wonder if we can query it?
- macOS with Qt 5.12 just lacks a few things, e.g. sensible default colour for the overview widget, and some custom widgets are a bit strangely rendered.