[Accessibility]: Tree page (pre-redesign): Focus lost when navigating from sidebar to page

Created by: umpox

Audit type

Keyboard navigation

User journey audit issue

https://github.com/sourcegraph/sourcegraph/issues/34420

Problem description

See how the focus is lost when navigating from the sidebar to the tree page. It takes about 4 presses of Tab before we finally reach "API Docs"

Expected behavior

We should expect that:

1. Focus is clear
2. The next tabbed item is the API Docs button (unless there's another appropriate item)

Additional details

No response

Assigning labels

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• If this issue will require input from designers in order to complete, please assign the label needs-design.
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Owner

This issue will be fixed by my team, I have assigned a relevant member to it, or I will do so in the near future.