public static setTheme(mode as String, theme as KssTheme) as Void:
Registers a loaded KSS theme.
Passing light or dark replaces the corresponding built-in slot. Passing system updates the currently effective system theme slot. Passing another name registers an application-specific theme without changing the built-in light and dark themes.
theme = KssTheme.load("themes/harbor.kss")
ThemeManager.setTheme("harbor", theme)
ThemeManager.setAppearanceMode("harbor")