Styles.swift

//
// Some styling architecture
//

class DefaultTheme {

    enum Color {
        static let primary: UIColor = .white
        static let secondary: UIColor = .gray
    }

}

class DarkTheme: DefaultTheme {

    enum Color {
        static let primary: UIColor = .black
    }

}

func main() {
    view.backgroundColor = DarkTheme.Color.secondary
}