How to indicate that a card is expandable?

1. What is a UX card?
2. What are cards in mobile design why are they good and when is the best time to use them?

What is a UX card?

So what's a card in UI/UX terms? The Nielsen Norman Group defines it as below: Definition: A card is a container for a few short, related pieces of information. It roughly resembles a playing card in size and shape, and is intended as a linked, short representation of a conceptual unit.

What are cards in mobile design why are they good and when is the best time to use them?

Cards are those little rectangles full of inclusive images and text that serve as entry points to more detailed information. They help designers to balance good interface aesthetics with good usability. The cards also very convenient and can be used for displaying content composed of different elements.