Add complete impl from codelabs github

lib/main.dart

@@ -43,7 +43,6 @@ class MyAppState extends ChangeNotifier {
     }
     notifyListeners();
   }
-
 }
 
 class MyHomePage extends StatefulWidget {
@@ -63,14 +62,16 @@ class _MyHomePageState extends State<MyHomePage> {
       case 1:
         page = FavoritesPage();
       default:
-        throw UnimplementedError('Unknown index: $selectedIndex');
+        throw UnimplementedError('no widget for $selectedIndex');
     }
+
+    return LayoutBuilder(builder: (context, constraints) {
       return Scaffold(
         body: Row(
           children: [
             SafeArea(
               child: NavigationRail(
-              extended: false,
+                extended: constraints.maxWidth >= 600,
                 destinations: [
                   NavigationRailDestination(
                     icon: Icon(Icons.home),
@@ -98,6 +99,7 @@ class _MyHomePageState extends State<MyHomePage> {
           ],
         ),
       );
+    });
   }
 }
 
@@ -145,7 +147,34 @@ class GeneratorPage extends StatelessWidget {
   }
 }
 
+class BigCard extends StatelessWidget {
+  const BigCard({
+    super.key,
+    required this.pair,
+  });
+
+  final WordPair pair;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final style = theme.textTheme.displayMedium!.copyWith(
+      color: theme.colorScheme.onPrimary,
+    );
 
+    return Card(
+      color: theme.colorScheme.primary,
+      child: Padding(
+        padding: const EdgeInsets.all(20),
+        child: Text(
+          pair.asLowerCase,
+          style: style,
+          semanticsLabel: "${pair.first} ${pair.second}",
+        ),
+      ),
+    );
+  }
+}
 
 class FavoritesPage extends StatelessWidget {
   @override
@@ -174,34 +203,3 @@ class FavoritesPage extends StatelessWidget {
     );
   }
 }
-
-
-
-class BigCard extends StatelessWidget {
-  const BigCard({
-    super.key,
-    required this.pair,
-  });
-
-  final WordPair pair;
-
-  @override
-  Widget build(BuildContext context) {
-    var theme = Theme.of(context);
-    var style = theme.textTheme.displayMedium!.copyWith(
-      color: theme.colorScheme.onPrimary,
-    );
-
-    return Card(
-      color: theme.colorScheme.primary,
-      child: Padding(
-        padding: const EdgeInsets.all(20),
-        child: Text(
-          pair.asLowerCase,
-          style: style,
-          semanticsLabel: pair.asPascalCase,
-          ),
-      ),
-    );
-  }
-}