[css-syntax-3][editorial] Fix heading

Author: tabatkins

css-syntax-3/Overview.bs

@@ -3443,8 +3443,8 @@ Defining Grammars for Rules and Other Values</h2>
 		all you have is the fact that there's a block and a function.
 	</div>
 
-<h3 id='declaration-rule-list'>
-Defining Block Contents: the <<declaration-list>>, <<rule-list>>, and <<stylesheet>> productions</h3>
+<h3 id='block-contents'>
+Defining Block Contents: the <<block-contents>>, <<declaration-list>>, <<qualified-rule-list>>, <<declaration-rule-list>>, and <<rule-list>> productions</h3>
 
 	The CSS parser is agnostic as to the contents of blocks--
 	they're all parsed with the same algorithm,