feat: update theme colors.

app/lib/themes/dark.dart

@@ -2,4 +2,6 @@ import 'package:flutter/material.dart';
 
 var darkTheme = ThemeData.dark().copyWith(
   primaryColor: Colors.grey,
+  scaffoldBackgroundColor: Color(0xff252525),
+  backgroundColor: Color(0xff282828),
 );

app/lib/themes/light.dart

@@ -2,4 +2,6 @@ import 'package:flutter/material.dart';
 
 var lightTheme = ThemeData.light().copyWith(
   primaryColor: Colors.blue,
-);
+  scaffoldBackgroundColor: Color(0xfff8f8f8),
+  backgroundColor: Color(0xffffffff),
+);