move folding example to fwe page

Author: schultek

site/lib/src/pages/custom_pages.dart

@@ -126,5 +126,55 @@ sitemap: false
 <ProgressRing progress="0.3" large />
 <ProgressRing progress="0.95" large />
 
+## Foldable Code Block
+
+```dart foldable showLineNumbers
+[* -
+import 'package:flutter/material.dart'; 
+import 'package:flutter/services.dart';
+*]
+
+void main() => runApp(const MyApp());
+
+class MyApp extends StatelessWidget {
+  const MyApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    [* -
+    return MaterialApp( // Root widget
+      home: Scaffold(
+        appBar: AppBar(
+          title: const Text('My Home Page'),
+        ),
+        body: Center(
+          [*
+          child: Builder(
+            builder: (context) {
+              return Column(
+                children: [
+                  const Text('Hello, World!'),
+                  [* -
+                  const SizedBox(height: 20),
+                  ElevatedButton(
+                    onPressed: () {
+                      print('Click!');
+                    },
+                    child: const Text('A button'),
+                  ),
+                  *]
+                ],
+              );
+            },
+          ),
+          *]
+        ),
+      ),
+    );
+    *]
+  }
+}
+```
+
 ''',
 );

src/content/get-started/fundamentals/widgets.md

@@ -38,11 +38,9 @@ can receive context from the parent.
 This structure carries all the way up to the root
 widget, as this trivial example shows:
 
-```dart foldable showLineNumbers
-[* -
-import 'package:flutter/material.dart'; 
+```dart
+import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-*]
 
 void main() => runApp(const MyApp());
 
@@ -51,37 +49,31 @@ class MyApp extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    [* -
     return MaterialApp( // Root widget
       home: Scaffold(
         appBar: AppBar(
           title: const Text('My Home Page'),
         ),
         body: Center(
-          [*
           child: Builder(
             builder: (context) {
               return Column(
                 children: [
                   const Text('Hello, World!'),
-                  [* -
                   const SizedBox(height: 20),
                   ElevatedButton(
                     onPressed: () {
                       print('Click!');
                     },
                     child: const Text('A button'),
                   ),
-                  *]
                 ],
               );
             },
           ),
-          *]
         ),
       ),
     );
-    *]
   }
 }
 ```