The eye separates an object from its background, and interfaces use that separation to signal layers.
UI foundation · Gestalt principles
Tag
depth
Entries tagged depth, drawn from across the library. Tags cut through the section structure, which is where most of the useful connections are.
2 entries across 1 section
Category
Level
2 entries
A system of layers that says what sits above what, expressed visually and enforced in code.
UI foundation · Form and depth