After a lot of feedback I encapsulated the Theme Switcher from my Alien Night Theme to this Theme Switcher Theme Component.
https://meta.discourse.org/t/how-do-i-install-a-theme-or-theme-component/63682
At the moment it will switch your theme into a dark mode (see Alien Night Preview). Later on I can maybe implement a setting page, where you can define just a global class to switch your theme into it.