[css-color-4][editorial] typo

Author: svgeesus

css-color-4/Overview.bs

@@ -640,7 +640,7 @@ Transparency: the 'opacity' property</h3>
 			rather than a particular color.
 
 			Opacity values outside the range [0,1] are not invalid,
-			and a preserved in specified values,
+			and are preserved in specified values,
 			but are clamped to the range [0, 1]
 			in computed values.
 	</dl>