Theme added to account settings

The Preferences card on your account page now has a Theme field (Light, Dark, or System) next to Language and Time zone.

At launch, it worked like the other two fields in that card: picking a theme didn't apply it, clicking the card's Save button did. That's different from the sidebar user menu's Theme submenu, which switched the instant you picked an option.

Theme is still a browser preference, not an account one: it isn't saved to your account and doesn't follow you to another browser or device, unlike Language and Time zone.