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

Author: tabatkins

css-syntax-3/Overview.bs

@@ -2288,7 +2288,7 @@ Parse a stylesheet's contents</h4>
 	</div>
 
 <h4 id="parse-block-contents" oldids="parse-list-of-declarations">
-Parse a list of declarations</h4>
+Parse a block's contents</h4>
 
 	<div algorithm>
 		To <dfn export>parse a block's contents</dfn> from |input|: