The evolution of Mac app window corners

"Each element is designed with a curvature that sits neatly within the corner radius of its container, in this case the window itself. And this relationship goes both ways. In the new design system, windows now have a softer, more generous corner radius, which varies based on the style of window. Windows with toolbars now use a larger radius, which is designed to wrap concentrically around the glass toolbar elements, scaling to match the size of the toolbar."

"These larger corners provide a softer feel and elegant concentricity to the window but they can also clip content that sits close to the edge of the window. To position content that nests into a corner, use the new NSView LayoutRegion API."

macOS Tahoe implements a new design system centered on concentricity, where window elements and containers align through matching curvature relationships. Windows now feature variable corner radiuses: larger radii for windows with toolbars to wrap around glass toolbar elements proportionally, and smaller radii for titlebar-only windows to fit compactly around window controls. This design approach creates a softer, more elegant aesthetic. However, the larger corner radiuses introduce a practical problem: content positioned near window edges risks being clipped. Apple addresses this issue by introducing the NSView LayoutRegion API, enabling developers to properly position content that nests into corners without clipping.

Read at Lapcatsoftware