On iPad / iPhone, the card background / frame are low resolution assets for all cards except the new Demon Hunter and dual class cards.
It affects only the card frame, not the actual card art or text.
It’s been like this for years now. Sure, not game-breaking, but these cards are really rather expensive - Don’t think it is too much to ask for them to look decent.
Unfortunately, other threads regarding this topic were unnoticed. Is there any other way to report stuff like this?