[css-contain] Fix typo

Author: mrego

css-contain-1/Overview.bs

@@ -168,7 +168,7 @@ Types of Containment</h2>
 	restricting the effects that its descendants can have on the rest of the page in various ways.
 	<a>Containment</a> enables much more powerful optimizations by user agents,
 	and helps authors compose their page out of functional units,
-	as it limits how widely an effect a given change can have on a document.
+	as it limits how widely a given change can affect a document.
 
 	Advisement: Specification authors introducing new properties or mechanisms
 	need to consider whether and how the various types of containment