Apple's new macOS 10.14 codename Mojave has a nice dark theme, but to change it you need to go click trough multiple screens to change the theme.
To switch fast and simple I created a Menu Bar App for this. It does exactly what you see below with a mouse click.
To switch theme, click left, to exit click right on the moon/sun icon.
You can download app it self DarkSome from my Blog and find futher instructions also there.
- Download DarkSome
- Unzip and place the app in Applications.
- Start the app.