The new "Confirm your email" email looks broken on Fastmail's webmail interface.
Link to email template for reference: https://gerrit.wikimedia.org/g/mediawiki/core/+/6b0d18ca14d1814238cbf45d8695b67c67cd735e/resources/templates/ConfirmEmail/EmailCreated.mustache
Fastmail applies some transformations to the HTML and the CSS to sanitize it. Here's the relevant part of the page it actually serves: P86734
Notably, the <body id="mw-confirm-email"> element from the email is nowhere to be found, and as a result none of the styles targeting #mw-confirm-email apply.
We should probably avoid relying on having any attributes on the body element, or on its existence. Just add another wrapper inside if you need to target styles at it.
