Mailchimp Block Button cannot be centered on old themes. Styling broken on newest themes.

[scosgro]

Steps to reproduce

1. Add a Mailchimp Block to a page, click on the button, and center it. Publish the page.

2. Activate an older theme (pre-Gutenberg). For example: Prosperity, Colinear, Revelar, Canape, Venture, Veggie, Appetite, Maisha, etc...

3. Refresh the page. The button will not be centered.
   

4. Activate a newer theme (block-based). For example: Balasana, Maywood, Rivington, Barnsbury

5. Refresh the page. The button will be centered (as it is in the editor):

6. Try an even newer theme. For example, Twenty Twenty, Seedlet, or Spearhead, and they'll come with their own formatting/stylistic issues for that same block:

What I expected

The Block to appear on the page styled like it is in the editor.

What happened instead

It varies. On our newest themes, the block's styling it all over the place. On older themes, it doesn't match the editor.

Browser / OS version

All

Screenshot / Video

Screenshots above.

Context / Source

Reported this as a theme bug here, but was told it was a block bug, so reposting here.

[scruffian]

This block lives in Jetpack so it probably should be logged there, sorry for the confusion.

[cathymcbride]

Moving to JP repo.

[jamiepalatnik]

Another report in 27847847-hc
Seems similar to this issue too: Automattic/themes#2892