added theme

lib/main.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 
+import 'theme.dart';
+
 void main() {
   runApp(const MyApp());
 }
@@ -11,11 +13,12 @@ class MyApp extends StatelessWidget {
   Widget build(BuildContext context) {
     return MaterialApp(
       title: 'Flutter Demo',
-      theme: ThemeData(
-        fontFamily: "Ubuntu",
-        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
-        useMaterial3: true,
-      ),
+      theme: lightTheme,
+      darkTheme: darkTheme,
+      home: Scaffold(
+          appBar: AppBar(
+        title: Text('ietn'),
+      )),
     );
   }
 }

lib/theme.dart

@@ -0,0 +1,19 @@
+import 'package:flutter/material.dart';
+
+final _baseTheme = ThemeData(
+  fontFamily: "Ubuntu",
+  useMaterial3: true,
+);
+
+final lightTheme = _baseTheme.copyWith(
+  colorScheme: ColorScheme.fromSeed(
+    seedColor: Colors.deepPurple,
+    brightness: Brightness.light,
+  ),
+);
+
+final darkTheme = _baseTheme.copyWith(
+    colorScheme: ColorScheme.fromSeed(
+  seedColor: Colors.purple.shade100,
+  brightness: Brightness.dark,
+));