Use constants

lib/ui/widgets/tablet_mode/appbar_custom_dropdown_widget.dart

@@ -5,6 +5,9 @@ import 'package:flutter/material.dart';
 ///
 /// @author Pierre Hubert
 
+const _overlay_w = 300.0;
+const _overlay_h = 400.0;
+
 class AppBarCustomDropDownWidget extends StatefulWidget {
   final Widget icon;
   final int notificationsBadge;
@@ -111,10 +114,10 @@ class _PopupContentBody extends StatelessWidget {
           child: Container(color: Color(0x55000000)),
         ),
         Positioned(
-          left: offset.dx - 300,
+          left: offset.dx - _overlay_w,
           top: offset.dy,
-          width: 300,
-          height: 400,
+          width: _overlay_w,
+          height: _overlay_h,
           child: Card(child: onBuild(context)),
         )
       ],