Style modal to look like a page [screenshot]

[hbillings]

We can make the modal feel like its own page, even though it isn't. This would help with continuity (if someone ctrl+clicks to open a new page, the experience is different; likewise if someone follows a link from an email we send).

The trickiest part of this would be not closing the modal when someone clicks on the background, but even that shouldn't be that hard.