Improve nav header behavior

[seancolsen]

Fixes #3287
Fixes #3899
Fixes #4048

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
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• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
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[pavish]

Looks good to me!