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What is CSS Outline Radius?

CSS outline radius describes rounded visual corners on an element’s outline. CSS has no widely supported standalone outline-radius property, so the rendered shape typically follows the element’s border radius.

How CSS Outline Radius works

An outline is painted around an element without participating in box dimensions, making it useful for focus indication without causing layout movement. Rounded controls complicate that geometry because the outline is outside the border edge and its curve is browser-rendered. In current CSS, authors combine outline, outline-offset, and border-radius; there is no standard outline-radius property to tune separately. This belongs in the interaction-state styling stage and needs cross-browser visual testing.

Key facts

  1. Unlike a border, an outline does not reserve space and may be non-rectangular; its exact drawing around fragmented or rounded boxes is not a substitute for layout geometry.
  2. outline-offset moves the outline away from or toward the border edge but does not define corner curvature, so it cannot independently specify a different outline radius.
  3. Removing the default focus outline without an equally visible replacement breaks keyboard orientation; clipping and low contrast should be checked at each control radius and zoom level.

When CSS Outline Radius matters

Check outline rendering when designing keyboard focus indicators for rounded buttons and controls. A browser may draw an outline differently from the border, so test visibility rather than assuming identical curves.

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