Reconsider the need for the lower, white navbar

[ang-zeyu]

Please confirm that you have searched existing issues in the repo

Yes, I have searched the existing issues

Any related issues?

Removes need for some of #1948

What is the area that this feature belongs to?

No response

Is your feature request related to a problem? Please describe.

The design lower navbar section containing the site and page nav buttons has some issues:

• While we have auto hide/show features for the header, the navbar does still take up some amount of space.
• There was some talk of FOUC coming from the lower section in the mobile header but I can't find that issue now. But that is another reason. FOUC happens due to performing style detection of whether we should show/hide the lower navbar based on the screen size.

Describe the solution you'd like

Some basic ideas for reference:

• FABs
  • a related ticket is Component-ify the back-to-top button #2081 (design should consider this)
• Reorganize the navbar to, somehow, contain all of (1) logo (2) nav items (3) search (4) site nav button (5) page nav button in mobile view.

First come up with a design, get input on it, then implement it.

Describe alternatives you've considered

No response

Additional context

No response

[ang-zeyu]

@jonahtanjz if you have any input

[jonahtanjz]

First come up with a design, get input on it, then implement it.

Some possible designs that we can consider - #980 (comment)