This guide is designed as a "get started" or introductory read for the starting to intermediate designer who wants to learn or get more knowledge about cross-DPI and cross-platform design from the very beginning.

There's no one best screen size to design for. Websites should transform responsively and fast at all screen resolutions on different browsers and platforms. Accessible. Mobile-friendly. Design for your audience, first. Design from 360x640 through 1920x1080.

Resolution independence is the notion that all graphics on a computer display should be zoomable to an arbitrary multiplier without losing quality. If you know even the slightest thing about computer graphics, you’ll understand that in a resolution independent world, bitmaps are out and vector graphics are in. Vector graphics can scale gracefully to an […]

We offer some advice for developers who are working with resolution independent applications.

[…] For the past few years, we have been anticipating the need for larger and larger graphics in user interfaces. This need is driven by displays with higher densities—in a few years time, our current 100 dpi displays will seem as quaint as a 640×480

Resolution Independent UI (Apple Developer)