https://developer.apple.com/videos/play/wwdc2025/310/?time=4...

> 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. Titlebar-only windows retain a smaller corner radius, wrapping compactly around the window controls. 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.