Grammar improvements for css-contain-2 (w3c#11540)

Author: Psychpsyo

css-contain-2/Overview.bs

@@ -852,12 +852,12 @@ Inline-Size Containment</h3>
 		but not in a way that reverts it to the previously-problematic layout.
 
 		For example, if scrollbars were introduced,
-		they are not then removed,
+		they are then not removed,
 		even if the consequent [=block size=] is small enough to not need them;
 		or if a box’s logical height collides with a lower-placed float and is cleared down
 		to where it also has more available inline space
 		and thus becomes short enough to not have collided,
-		it is not them moved back up to its previous problematic size and position.
+		it is then not moved back up to its previous problematic size and position.
 
 		Thus, although [=inline-size containment=] prevents
 		the box’s content from directly affecting its [=inline size=]