[Feature request] Nested navigation tabs

[couleurm]

Hey, the navigation tab offer quite a bit of horizontal estate to quickly get started, though I'd like to expand further and have them nested, is that something plausible?

Here's how I imagine it could be configured (could be prettier):

nav:

  # ...

  - Video:
    - __nestlevel__: 2
    - Setup: video/index.md
      # ...
    - Content creation: video/index.md
      # ...
    - Video Editing:
      # ...

[squidfunk]

This could be implemented with theme extension, but will need some CSS knowledge to pull off. We're currently not considering adding this functionality to the theme because of its limited use and as navigation is already quite complex.

[couleurm]

If you'd like to try it out, Hybrid makes full on use of this UI strategy (at the cost of aesthetics and being a bit confusing at first)