Shape and density
Shape expresses attachment and grouping while preserving stable target geometry.
Radius scale
None 0px; micro 2px; small 4px; control 6px; card and window 8px; surface 12px; showcase 16px; pill 999px. Square edges that meet a monitor, taskbar or adjoining pane.
Spacing
The spacing scale is 0, 2, 4, 6, 8, 12, 16, 20, 24, 32, 40, 48 and 64px. Related groups use 16px, major groups 24px, and controls reserve 6px for focus paint.
Density and targets
Comfortable one-line controls are at least 36px high, compact controls 32px and coarse-pointer controls 44px. Search fields are at least 44px, 40px and 44px respectively. Content may increase these sizes; compact density does not shrink text.
Popup and taskbar geometry
Detached popups use 12px free corners and a 16px alignment inset, or 12px in narrow layouts. The taskbar height is calc(3rem + 8px), with scrolling to preserve controls and focus rings. Snapped and maximized clients have square corners.