Theme Change
theme-change feature is used to enable system theme change related types and event builder. It is suitable for when the system switches from light mode to dark mode, updating the application theme or rebuilding related styles.
Event Entry
After enabling feature, can use on_theme_changed(...):
ThemeMode currently has two values:
Complete signature and current dispatch status see Handler API's Theme Change Events. If you only need normal view state styles, don't need to enable this feature; it faces system theme change.

