The negative margin was causing it to overlap the previous header

Fixed css .search-active.main

Improve accessibility by adding label to Anchor links.

I ran Lighthouse on just-the-docs and noticed the anchor links
were missing a "discernible name".

This adds aria-labelledby to the header element to improve these for
screenreaders.

Remove collapsible TOC on nav doc

Pdmosses collapsible toc

Merge branch 'collapsible-toc' of git://github.com/pdmosses/just-the-docs into pdmosses-collapsible-toc

Bump @primer/css from 14.3.0 to 14.4.0

Bump stylelint from 13.3.3 to 13.6.1

Bump stylelint-config-prettier from 8.0.1 to 8.0.2

Bumps [@primer/css](https://github.com/primer/css) from 14.3.0 to 14.4.0.
- [Release notes](https://github.com/primer/css/releases)
- [Changelog](https://github.com/primer/css/blob/master/CHANGELOG.md)
- [Commits](https://github.com/primer/css/compare/v14.3.0...v14.4.0

)

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