[css-content-3] Improve cross-reference.

Author: fantasai

css-content-3/Overview.bs

@@ -1203,10 +1203,10 @@ The ''content()'' function</h4>
 	</div>
 
 
-<h2 id="counters">
-Automatic Counters and Numbering</h2>
+<h3 id="counters">
+Automatic Counters and Numbering</h3>
 
-	See [[!CSS-LISTS-3]].
+	See [[css-lists-3#auto-numbering]].
 
 	Issue: Should this move back to CSS Content?