[css-values] typo

Author: tabatkins

css-values-4/Overview.bs

@@ -1744,7 +1744,7 @@ Type Checking</h4>
 		can be used in 'width'.
 	</div>
 
-	Additionally, [=math function=] that resolve to <<number>>
+	Additionally, [=math functions=] that resolve to <<number>>
 	can be used in any place that only accepts <<integer>>.
 	(It gets rounded to the nearest integer,
 	as specified in [[#calc-range]].)