Improve `:focus` styles by making the same as `:hover` styles

This improves the focus styles for Buttons and Menus by making them the same as what what gets applied on hover.

I changed the Buttons styles to have more slightly contrast when hovered/focused so that we could remove the ugly and inconsistent focus outlines. **Note:** that the focus outlines still exist for Menus.

The Buttons and Menus test HTML pages can loaded up in a browser and tabbing around shows the improved result of these changes.