Enhancement: Button styling

Button styling (colors and hover colors) has been improved in both light and dark mode to be more consistent among various button styles (colors for filled and outline buttons)

https://github.com/owncloud/web/pull/9394
https://github.com/owncloud/web/pull/9459
https://github.com/owncloud/web/issues/9353
https://github.com/owncloud/web/issues/9354
