Function
The card is relative overflow-hidden so that AccountWait's beam, which
the form inside renders while its request is in flight, anchors to the card's
top edge and is clipped by its rounded corners. That is the only reason for
those two classes; the shell itself knows nothing about the wait and stays a
server component.
The card every account page is built in: sign-in, sign-up, forgot and reset password. A heading, an optional subtitle, the page's content, and a footer for the links between those pages.