Improvements to hover/active/focus states in header items

What does this MR do?

Adds some improvements to buttons, dropdowns, inputs, etc. in the header area.

Are there points in the code the reviewer needs to double check?

I'm not sure.

Why was this MR needed?

Requested in an issue.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #24202 (closed)

This is not complete yet. I'm new to this, so please let me know what all steps do I need to do (tests, changelog, etc.).