[css-ui-4] Outlines follow corner shapes

See #12194

Author: frivoal

css-ui-4/Overview.bs

@@ -320,7 +320,8 @@ Outline properties</h2>
 
 	The parts of the outline are not required to be rectangular.
 	To the extent that the outline follows the <a>border edge</a>,
-	it should follow the 'border-radius' curve.
+	it should follow the 'border-radius' curve,
+	as was as the 'corner-shape'.
 
 	The position of the outline may be affected by descendant boxes.