Site Editor Compatibility: Mailchimp Block styling issues in front end

[andrewserong]

In the new site editor in Gutenberg (/wp-admin/admin.php?page=gutenberg-edit-site), there are some issues with the Mailchimp block within the front end of the site.

Steps to reproduce the issue

1. With the Gutenberg plugin active (>=10.4.0-rc1), activate a block-ready theme (like tt1-blocks)
2. In the site editor, insert a Mailchimp block into the Footer template part
3. Go through the flow to connect your Mailchimp account and set Mailchimp to add to one of your lists
4. Save the Footer template part and view the front end of your site

What I expected

For the input field and button to render consistently with how the block is displayed in the post/page editor in the Twenty Twenty theme

What happened instead

The input field and button block appear to receive no direct styling by the block.

This issue appears to be quite similar to the issues with the Contact Form #19462 and Jetpack Button blocks #19464

Expected (Twenty Twenty Theme)

Note that even in the expected styling, there are still issues in the Twenty Twenty theme (the input field isn't full width / doesn't appear to support width settings, no margin on the button).

Actual result in FSE (tt1-blocks theme applied)