The account menu has a Theme row of System, Light, and Dark buttons between Admin and Sign out, set apart by a separator above and below, so the scheme can be switched without opening Settings. It is the same device-only choice as Preferences, read from one list in shared/theme.ts, and the menu stays open after a pick so the change shows behind it. Separator is a new shared hairline, one device pixel at 2x, in the new separator color, and monitor, sun, moon, and contrast icons are drawn in the puffy style.