WIP: Resolve "Make the focus visible during tabbing"

Make the focus visible during tabbing

On the front page, all buttons have a visual response when they are focused.
On the user page, the buttons to enter previously joined rooms have a visual response.
All header buttons are bordered while focused. All footer buttons change their color to the contrast color.
Menu items have a slightly different color when focused, except the theme menu items, because they can not be focused at the moment.