Hi again.
Unfortunately, you are not able to completly replace a button on the Universal Login Page. I can see on Intuit’s developer page that it specifies:
If your application is spaced constrained and you must use an icon
You cannot remove the icon from a social/enterprise connection unfortunately, and from what I understand from Intuit’s page, it does allow you to use their logo in some situations.
For the font, you cannot customize it to be specific to the button, you should be able to customize the font via the Dashboard under Branding → Universal Login → Customization Options → Fonts.
Otherwise, social/enterprise connection buttons do not have the option to customize the padding/margin directly. You might want to look into Customizing the Universal Login Page Templates. I believe you should be able to customize the margin and padding of the text available inside the buttons under the Prompts → login section.
This might be helpful in accomplishing the customization of the text.
If I can help with anything else, let me know!
Kind Regards,
Nik