[css-backgrounds-3] Cross link to 'ink overflow' terminology for box-shadow also

Author: fantasai

css-backgrounds-3/Overview.bs

@@ -2739,7 +2739,8 @@ Layering, Layout, and Other Details</h4>
 	If the affected box has multiple fragments,
 	the shadows are applied as specified in 'box-decoration-break'.
 
-	Shadows do not trigger scrolling or increase the size of the [=scrollable overflow area=].
+	Shadows are [=ink overflow=];
+	they do not trigger scrolling or increase the size of the [=scrollable overflow area=].
 
 	Outer shadows have no effect on internal table elements in the collapsing border model.
 	If a shadow is defined for single border edge in the collapsing border model