uui-button: primary buttons and focus issues

[iOvergaard]

Have a look here at the different button looks. https://uui.umbraco.com/?path=/docs/uui-button--docs

When look is "primary" it is very difficult to see the button has focus, but when hover the button, it's a bit more clear the button has focus.

Originally posted by @bjarnef in https://github.com/umbraco/Umbraco-CMS/issues/15078#issuecomment-1790903168