Card themes

theme accepts tg2-light (default), tg2-dark, tg-light and tg-dark. grey is a tg2-only surface — under tg-light / tg-dark it resolves to the same colour as white rather than throwing, so the input is inert there instead of broken.

radius resolves per theme. tg2-light / tg2-dark use the new scale; tg-light / tg-dark use the radii the legacy card is given in FrEnd today, and default to large (8px) so an unmigrated page keeps the legacy card's corner.