Fix broken link to css-backgrounds-3 corner clipping

Author: Psychpsyo

css-contain-2/Overview.bs

@@ -1392,7 +1392,7 @@ Paint Containment</h3>
 	1. The contents of the element
 		including any [=ink overflow|ink=] or [=scrollable overflow=]
 		must be clipped to the <a>overflow clip edge</a> of the [=paint containment box=],
-		taking [[css-backgrounds-3#corner clipping|corner clipping]] into account.
+		taking [[css-backgrounds-3#corner-clipping|corner clipping]] into account.
 		This does not include the creation of any mechanism
 		to access or indicate the presence of the clipped content;
 		nor does it inhibit the creation of any such mechanism through other properties,