Remove Extend section from documentation

Co-authored-by: mdo <98681+mdo@users.noreply.github.com>

Author: Copilot

package-lock.json

@@ -186,13 +186,6 @@
         - title: Opacity
         - title: Shadows
 
-- title: Extend
-  icon: tools
-  icon_color: blue
-  pages:
-    - title: Approach
-    - title: Icons
-
 - title: About
   icon: globe2
   icon_color: indigo

site/data/sidebar.yml

@@ -30,7 +30,7 @@ Read about them in the [`z-index` layout page]([[docsref:/layout/z-index]]).
 
 On some components, we use our low-level `z-index` values to manage repeating elements that overlap one another (like buttons in a button group or items in a list group).
 
-Learn about our [`z-index` approach]([[docsref:/extend/approach#z-index-scales]]).
+Learn about our [`z-index` approach]([[docsref:/layout/z-index]]).
 
 ## CSS