fix :focus styles for selected filter dropdown items

What does this MR do?

• update styles to out-specificity-ify those in dropdowns.scss
• move padding from li to .btn
• fix focus styles
• remove focus outline

Screenshots (if relevant)

focus, hover and active all share this style now:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] 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 #35482 (closed)