Set the background color for progress dialog

lib/utils/dialog_util.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:photos/ui/loading_widget.dart';
 import 'package:progress_dialog/progress_dialog.dart';
@@ -10,6 +11,8 @@ ProgressDialog createProgressDialog(BuildContext context, String message) {
   );
   dialog.style(
     message: message,
+    messageTextStyle: TextStyle(color: Colors.white),
+    backgroundColor: Colors.grey[850],
     progressWidget: loadWidget,
     borderRadius: 4.0,
     elevation: 10.0,