Refactored several theme settings into custom theme

lib/presentation/views/main_menu/group_view/create_group_view.dart

@@ -52,7 +52,7 @@ class _CreateGroupViewState extends State<CreateGroupView> {
           mainAxisAlignment: MainAxisAlignment.start,
           children: [
             Container(
-              margin: const EdgeInsets.symmetric(horizontal: 12, vertical: 10),
+              margin: CustomTheme.standardMargin,
               child: TextInputField(
                 controller: _groupNameController,
                 hintText: loc.group_name,

lib/presentation/views/main_menu/match_view/create_match/create_match_view.dart

@@ -127,7 +127,7 @@ class _CreateMatchViewState extends State<CreateMatchView> {
           mainAxisAlignment: MainAxisAlignment.start,
           children: [
             Container(
-              margin: const EdgeInsets.symmetric(horizontal: 12, vertical: 5),
+              margin: CustomTheme.tileMargin,
               child: TextInputField(
                 controller: _matchNameController,
                 hintText: hintText ?? '',

lib/presentation/views/main_menu/statistics_view.dart

@@ -57,7 +57,7 @@ class _StatisticsViewState extends State<StatisticsView> {
                           width: constraints.maxWidth * 0.95,
                           values: winCounts,
                           itemCount: 3,
-                          barColor: Colors.blue,
+                          barColor: Colors.green,
                         ),
                         SizedBox(height: constraints.maxHeight * 0.02),
                         StatisticsTile(
@@ -75,7 +75,7 @@ class _StatisticsViewState extends State<StatisticsView> {
                           width: constraints.maxWidth * 0.95,
                           values: matchCounts,
                           itemCount: 10,
-                          barColor: Colors.green,
+                          barColor: Colors.blue,
                         ),
                       ],
                     ),