There is a basic Mailchimp signup Bric, that @norm made as an example for the Developer API, shown recently in this thread. It can be accessed via Developer > Bric Builder, in the top menu bar of the app. Once in the Bric Builder ‘add new Bric’ menu (+).
It looks as follows in Blocs:
Bric Library:
Used on Page:
Side Bar Options:
Otherwise …
Via Blocs Preview? Does it look ok when previewed directly in a Browser?