Collapse header categories in new 1.0 nav bar?

[olivekl]

The new nav bar for v1.0 is very long.

There's a limit to how much information someone can absorb, so I think it'd be good to collapse the headings with indented links underneath. So Understanding SLSA, Specification, Attestations, and How to SLSA could all be collapsed, to expand when clicked.

Is that possible?