Flat design is the visual language that took over screens around 2012-2013, when Microsoft's Metro interface, Apple's iOS 7 redesign, and Google's Material Design all shed the glossy, textured 'skeuomorphism' (interfaces imitating real objects) that had dominated early smartphones. Its principles: no drop shadows, no bevels, no photographic textures - just clean geometry, bold solid color, crisp typography, and simple, scalable iconography. The motivation was partly practical (scales beautifully across screen sizes and resolutions, loads fast) and partly philosophical (let the content, not the chrome, speak). Its commercial descendants include the ubiquitous tech-illustration styles of the late 2010s.
LibreOffice flat icon set - solid color, simple geometry, no texture or gloss.CC0 (The Document Foundation) · source
Defining characteristics
No skeuomorphic effects: zero shadows, bevels, gradients, or textures
Bright, solid color palettes with strong contrast
Simple geometric shapes and bold, minimal iconography
Typography-forward hierarchy; generous whitespace
Grid-based, scalable layouts that survive any screen size
Emphasis on usability and content over ornament
Key figures
Microsoft Metro design language(2010-2015) — The early mainstream flat UI (Windows Phone, Windows 8)
Apple iOS 7 redesign(2013) — The tipping point that made flat the industry default
Google Material Design(2014) — Systematized flat design with a subtle, principled use of depth