[css-nesting-1] Use the new <<style-block>> production.

Author: tabatkins

css-nesting-1/Overview.bs

@@ -390,7 +390,7 @@ The Nesting At-Rule: ''@nest'' {#at-nest}
 	Its syntax is:
 
 	<pre class=prod>
-		<dfn>@nest</dfn> = @nest <<selector-list>> { <<declaration-list>> }
+		<dfn>@nest</dfn> = @nest <<selector-list>> { <<style-block>> }
 	</pre>
 
 	The ''@nest'' rule is only valid inside of a [=style rule=].
@@ -522,7 +522,8 @@ Nesting Conditional Rules {#conditionals}
 	inside of [=style rules=].
 
 	When nested in this way,
-	the contents of a [=conditional group rule=] are parsed the same as a [=style rule's=] contents:
+	the contents of a [=conditional group rule=] are parsed as <<style-block>>
+	rather than <<stylesheet>>:
 
 	* Properties can be directly used,
 		applying to the same elements as the parent rule