enhancement: dark theme

[Matt P]

provide the option for a dark theme (quick! before i go blind) :)

[Thomas Nairn]

The ability and an example Dark theme is available in V4.0.0
See theming:
https://github.com/plugsy/core/blob/main/docs/theming.md

[Matt P]

@Inlustra Thanks. that's a nice feature.
Slate