Add formatting settings

[seankwilliams]

This request was from the thread at https://wordpress.org/support/topic/button-of-rich-text-dont-work-correctly/#post-12050935:

Make it possible to change the font (size, font, bolt, italic etc.), as well as a pop-up window (size, background, borders, etc.)

[larsschellhas]

I would like to add the general appearance of the footnote like a surrounding circle/square and its background colour. :)

[seankwilliams]

@larsschellhas - Noted, those would be good styles to allow customizing!