Card Systems, Containers, and Surface Elevation Hierarchy

Cards have become the universal metaphor for content modularity across responsive web and mobile interfaces:

• Metaphor: A card represents a single conceptual unit of content (e.g., a product, a user profile, an article).
• Self-Contained Ergonomics: Cards can be easily rearranged, filtered, stacked, and translated across breakpoints without breaking page cohesion.
• Elevation Hierarchy: Modern design systems use z-index elevation planes (Z0 base canvas, Z1 raised card, Z2 floating popover, Z3 modal overlay) paired with progressive shadow blur to communicate spatial depth and modal focus.