card background
One or more cards are part of the background.
Don't confuse this tag with card (medium). See the examples:
- Danbooru post #1033743 (card background, not card (medium), because cards are in the background)
- Danbooru post #887904 (card (medium), not card background, because the image is a card)
- Danbooru post #936083 (both card background and card (medium), as they overlap)