[css-overflow-3][editorial] Add parens w3c#7511

Author: fantasai

css-overflow-3/Overview.bs

@@ -270,7 +270,7 @@ Scrollable Overflow</h3>
 			within the [=scrollable overflow rectangle=],
 			the box’s own padding
 			so that when its content is scrolled to the end,
-			there is padding between the end-edge of its in-flow or floated content
+			there is padding between the end-edge of its in-flow (or floated) content
 			and the border edge of the box.
 			It typically ends up being exactly the same size as the box's own padding,
 			except in a few cases--