I'm hoping there's a cleaner way to do this than adding a CSS file (and therefore an HTTP request) for mobile, but overriding the entire stylesheet does seem a bit overkill, eh? Maybe we can reverse the roles and assume "default" viewtype is mobile-first, then if it's not mobile, add a stylesheet for "desktop"?

Open to other ideas, too. Sorry to complicate things, but since we have to go through deprecation if we want to change anything, it's probably best to do the extra work to get things right the first time...