[css-containment] Fix markup

Author: tabatkins

css-containment/Overview.bs

@@ -48,7 +48,7 @@ Strong Containment: the 'contain' property</h2>
 	and allows authors to be confident that their page won't accidentally fall into a slow code path
 	due to an innocuous change.
 
-	<dl dfn-type=value dfn-for=containment>
+	<dl dfn-type=value dfn-for=contain>
 		<dt><dfn>none</dfn>
 		<dd>
 			This value indicates that the property has no effect.
@@ -57,7 +57,7 @@ Strong Containment: the 'contain' property</h2>
 
 		<dt><dfn>strict</dfn>
 		<dd>
-			The ''containment/strict'' value indicates that the element is <a>strictly contained</a>,
+			The ''contain/strict'' value indicates that the element is <a>strictly contained</a>,
 			so that its contents are guaranteed to have no effect on the rest of the page outside the element's bounds.
 	</dl>
 
@@ -72,7 +72,7 @@ Strong Containment: the 'contain' property</h2>
 
 		For example, assume a micropost social network had markup something like this:
 
-		<pre class='css'>
+		<pre class='lang-css'>
 			&lt;body>
 				&lt;aside class='sidebar'>...&lt;/aside>
 				&lt;article class='messages'>