`RTheme` class

public static class RTheme

The theme of the application: light, dark or as the system.

Properties

static RThemeMode Mode { get; set; }: The choice in use; setting it changes the theme of the application.
static bool IsDark { get; }: Whether the theme on the screen now is dark (also when chosen by the system).

static void Toggle(): Light ↔ dark, from the theme on the screen (a System choice becomes the other).
static void Remember(RSettings s, string key = "ui.theme", RThemeMode def = System): Reads the choice from the settings (the default if missing), applies it, and writes it there at every change.
static void Fill(MenuItem menu): Fills a menu with the three choices (texts of RLang, «raval.theme.*»), the one in use ticked.
static Button Button(): A flat button with sun or moon that toggles light and dark.

event Action<RThemeMode> Changed: After the theme has changed, with the new choice.