pub fn set_app_theme(theme: Theme)Expand description
Force the app’s active Theme, overriding whatever the platform’s own
light/dark preference would otherwise select — reaching BOTH delivery paths
(widget paint/layout via RenderRoot::set_theme, and use_context::<Theme>()
via provide_context) the next time the running shell polls
ThemeOverrideWatcher::poll (once per frame — see the module docs).
Callable from any thread (see the module docs’ thread contract); the
process-wide slot is a plain Mutex, not a UI-thread-only primitive.