Added navigation. Very nice!! ;D

lib/main.dart

@@ -13,21 +13,98 @@ class MainApp extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-
     return MaterialApp(
-        title: 'Recurring Expense Tracker',
+      title: 'Recurring Expense Tracker',
-        theme: ThemeData(
+      theme: ThemeData(
-          useMaterial3: true,
+        useMaterial3: true,
-          colorScheme: ColorScheme.fromSeed(seedColor: Colors.green),
+        colorScheme: ColorScheme.fromSeed(seedColor: Colors.green),
-        ),
-        home: Scaffold(
-        body: ExpenseInputForm(),
-        //floatingActionButton: IconButton(onPressed: appState.newExpense(), icon: Icon(Icons.add)),
       ),
+      home: HomePage(),
     );
   }
 }
 
+class HomePage extends StatefulWidget {
+  const HomePage({
+    super.key,
+  });
+
+  @override
+  State<HomePage> createState() => _HomePageState();
+}
+
+class _HomePageState extends State<HomePage> {
+  var pageSelected = 0;
+
+  @override
+  Widget build(BuildContext context) {
+    Widget page;
+    switch (pageSelected) {
+      case 0:
+        page = ExpenseInputForm();
+      case 1:
+        page = Placeholder();
+      case 2:
+        page = Placeholder();
+      case 3:
+        page = Placeholder();
+      case 4:
+        page = Placeholder();
+      default:
+        throw UnimplementedError('no widget for $pageSelected');
+    }
+
+    return LayoutBuilder(builder: (context, constraints) {
+      return Scaffold(
+        body: Row(
+          children: [
+            SafeArea(
+              child: NavigationRail(
+                extended: constraints.maxWidth >= 600,
+                destinations: [
+                  NavigationRailDestination(
+                    icon: Icon(Icons.payment),
+                    label: Text('Expenses'),
+                  ),
+                  NavigationRailDestination(
+                    icon: Icon(Icons.account_balance),
+                    label: Text('Income'),
+                  ),
+                  NavigationRailDestination(
+                    icon: Icon(Icons.attach_money),
+                    label: Text('Liquid Assets'),
+                  ),
+                  NavigationRailDestination(
+                    icon: Icon(Icons.bar_chart),
+                    label: Text('Projections'),
+                  ),
+                  NavigationRailDestination(
+                    icon: Icon(Icons.settings),
+                    label: Text('Settings'),
+                  ),
+                ],
+                selectedIndex: pageSelected,
+                onDestinationSelected: (value) {
+                  setState(() {
+                    pageSelected = value;
+                  });
+                },
+              ),
+            ),
+            Expanded(
+              child: Container(
+                color: Theme.of(context).colorScheme.primaryContainer,
+                child: page,
+              ),
+            ),
+          ],
+        ),
+        //floatingActionButton: IconButton(onPressed: appState.newExpense(), icon: Icon(Icons.add)),
+      );
+    });
+  }
+}
+
 class ExpenseInputForm extends StatefulWidget {
   const ExpenseInputForm({
     super.key,
@@ -71,8 +148,8 @@ class _ExpenseInputFormState extends State<ExpenseInputForm> {
           height: inputHeight,
           child: TextField(
             keyboardType: TextInputType.numberWithOptions(decimal: true),
-            decoration: InputDecoration(
+            decoration:
-                labelText: "Cost", hintText: "Example: 10.00"),
+                InputDecoration(labelText: "Cost", hintText: "Example: 10.00"),
           ),
         ),
         DropdownMenu(
@@ -88,9 +165,7 @@ class _ExpenseInputFormState extends State<ExpenseInputForm> {
               keyboardType: TextInputType.text,
               decoration: InputDecoration(
                   labelText: "Description",
-                  hintText:
+                  hintText: "Example: 1GB data with unlimited talk & text."),
-                      "Example: 1GB data with unlimited talk & text."
-                ),
             )),
       ]),
     );