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

[scosgro]

Per Slack comment, I've reposted to Create in Calypso, here: https://github.com/Automattic/wp-calypso/issues/48392

Steps to replicate

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:

Result

Different results, depending on the themes. Older themes can't center the button. Newer themes look altogether broken.

Expected

The Mailchimp Block to appear styled as it does in the editor for the page.

[scruffian]

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