Added Dark theme with toggle to switch

Moved all Color variables to Styles.dart
Now saves current theme locally for subsequent runs
Saves it automatically every time you change it
Default at first run is Dark theme
FAB labels don't support theming yet, will be added if (fysoul17/flutter_speed_dial_material_design#7) is merged

sudoku/lib/Alerts.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'main.dart';
+import 'package:sudoku/Styles.dart';
 
 class AlertGameOver extends StatelessWidget {
   static bool newGame = false;
@@ -10,19 +10,26 @@ class AlertGameOver extends StatelessWidget {
   Widget build(BuildContext context) {
     return AlertDialog(
       shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
-      title: Text('Game Over'),
-      content: Text('You successfully solved the Sudoku'),
+      backgroundColor: Styles.bg_2,
+      title: Text(
+        'Game Over',
+        style: TextStyle(color: Styles.fg),
+      ),
+      content: Text(
+        'You successfully solved the Sudoku',
+        style: TextStyle(color: Styles.fg),
+      ),
       actions: [
         FlatButton(
-          textColor: MyApp.primaryColor,
+          textColor: Styles.primaryColor,
           onPressed: () {
             Navigator.pop(context);
             restartGame = true;
           },
           child: Text('Restart Game'),
         ),
         FlatButton(
-          textColor: MyApp.primaryColor,
+          textColor: Styles.primaryColor,
           onPressed: () {
             Navigator.pop(context);
             newGame = true;
@@ -72,7 +79,12 @@ class AlertDifficulty extends State<AlertDifficultyState> {
   Widget build(BuildContext context) {
     return SimpleDialog(
       shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
-      title: Center(child: Text('Select Difficulty Level')),
+      title: Center(
+          child: Text(
+        'Select Difficulty Level',
+        style: TextStyle(color: Styles.fg),
+      )),
+      backgroundColor: Styles.bg_2,
       contentPadding: EdgeInsets.fromLTRB(10, 10, 10, 10),
       children: <Widget>[
         for (String level in difficulties)
@@ -90,8 +102,8 @@ class AlertDifficulty extends State<AlertDifficultyState> {
                 style: TextStyle(
                     fontSize: 15,
                     color: level == this.currentDifficultyLevel
-                        ? MyApp.primaryColor
-                        : Colors.black)),
+                        ? Styles.primaryColor
+                        : Styles.fg)),
           ),
       ],
     );
@@ -103,18 +115,25 @@ class AlertExit extends StatelessWidget {
   Widget build(BuildContext context) {
     return AlertDialog(
       shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
-      title: Text('Exit Game'),
-      content: Text('Are you sure you want to exit the game ?'),
+      backgroundColor: Styles.bg_2,
+      title: Text(
+        'Exit Game',
+        style: TextStyle(color: Styles.fg),
+      ),
+      content: Text(
+        'Are you sure you want to exit the game ?',
+        style: TextStyle(color: Styles.fg),
+      ),
       actions: [
         FlatButton(
-          textColor: MyApp.primaryColor,
+          textColor: Styles.primaryColor,
           onPressed: () {
             Navigator.pop(context);
           },
           child: Text('No'),
         ),
         FlatButton(
-          textColor: MyApp.primaryColor,
+          textColor: Styles.primaryColor,
           onPressed: () {
             SystemNavigator.pop();
           },
@@ -159,12 +178,12 @@ class AlertNumbers extends State<AlertNumbersState> {
                 Navigator.pop(context);
               })
             },
-            color: Colors.white,
-            textColor: MyApp.primaryColor,
+            color: Styles.bg_2,
+            textColor: Styles.primaryColor,
             highlightColor: Colors.blueAccent,
             shape: RoundedRectangleBorder(
                 side: BorderSide(
-                  color: Colors.black,
+                  color: Styles.fg,
                   width: 1,
                   style: BorderStyle.solid,
                 ),
@@ -199,7 +218,12 @@ class AlertNumbers extends State<AlertNumbersState> {
   Widget build(BuildContext context) {
     return AlertDialog(
         shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
-        title: Center(child: Text('Choose a Number')),
+        backgroundColor: Styles.bg_2,
+        title: Center(
+            child: Text(
+          'Choose a Number',
+          style: TextStyle(color: Styles.fg),
+        )),
         content: Column(
           mainAxisSize: MainAxisSize.min,
           mainAxisAlignment: MainAxisAlignment.center,

sudoku/lib/Styles.dart

@@ -0,0 +1,77 @@
+import 'package:flutter/material.dart';
+
+class Styles {
+  // #121212
+  static MaterialColor dark = MaterialColor(4279374354, {
+    50: Color(0xff7d7d7d),
+    100: Color(0xff717171),
+    200: Color(0xff595959),
+    300: Color(0xff414141),
+    400: Color(0xff2a2a2a),
+    500: Color(0xff121212),
+    600: Color(0xff101010),
+    700: Color(0xff0e0e0e),
+    800: Color(0xff0d0d0d),
+    900: Color(0xff0b0b0b)
+  });
+
+  // #FFFFFF
+  static MaterialColor light = MaterialColor(4294967295, {
+    50: Color(0xffffffff),
+    100: Color(0xffffffff),
+    200: Color(0xffffffff),
+    300: Color(0xffffffff),
+    400: Color(0xffffffff),
+    500: Color(0xffffffff),
+    600: Color(0xffe5e5e5),
+    700: Color(0xffcccccc),
+    800: Color(0xffb2b2b2),
+    900: Color(0xff999999)
+  });
+
+  // 303030
+  static MaterialColor grey = MaterialColor(4281348144, {
+    50: Color(0xff8d8d8d),
+    100: Color(0xff838383),
+    200: Color(0xff6e6e6e),
+    300: Color(0xff595959),
+    400: Color(0xff454545),
+    500: Color(0xff303030),
+    600: Color(0xff2b2b2b),
+    700: Color(0xff262626),
+    800: Color(0xff222222),
+    900: Color(0xff1d1d1d)
+  });
+
+  // #3880ff
+  static MaterialColor primaryColor = MaterialColor(4281893119, {
+    50: Color(0xff92b9ff),
+    100: Color(0xff88b3ff),
+    200: Color(0xff74a6ff),
+    300: Color(0xff6099ff),
+    400: Color(0xff4c8dff),
+    500: Color(0xff3880ff),
+    600: Color(0xff3273e5),
+    700: Color(0xff2d66cc),
+    800: Color(0xff275ab2),
+    900: Color(0xff224d99)
+  });
+
+  // #eb445a
+  static MaterialColor secondaryColor = MaterialColor(4293608538, {
+    50: Color(0xfff498a4),
+    100: Color(0xfff38f9c),
+    200: Color(0xfff17c8c),
+    300: Color(0xffef697b),
+    400: Color(0xffed576a),
+    500: Color(0xffeb445a),
+    600: Color(0xffd33d51),
+    700: Color(0xffbc3648),
+    800: Color(0xffa4303f),
+    900: Color(0xff8d2936)
+  });
+
+  static MaterialColor bg = dark;
+  static MaterialColor bg_2 = grey;
+  static MaterialColor fg = light;
+}