Improve group page

lib/ui/screens/authorized_group_page_screen.dart

@@ -50,19 +50,19 @@ class _AuthorizedGroupPageScreenState
   List<_GroupPageTab> get _tabs => [
         // Posts list
         _GroupPageTab(
-          widget: GroupPostsSection(group: _group),
+          widget: (c) => GroupPostsSection(group: _group),
           label: tr("Posts"),
         ),
 
         // About the group
         _GroupPageTab(
-          widget: AboutGroupSection(group: _group),
+          widget: (c) => AboutGroupSection(group: _group),
           label: tr("About"),
         )
       ]..addAll(_group.isAtLeastModerator
           ? [
               _GroupPageTab(
-                widget: GroupMembersSection(groupID: _group.id),
+                widget: (c) => GroupMembersSection(groupID: _group.id),
                 label: tr("Members"),
               ),
             ]
@@ -91,7 +91,7 @@ class _AuthorizedGroupPageScreenState
       child: Column(
         children: [
           _buildGroupPageHeader(),
-          Container(
+          Material(
             color: _headerColor,
             child: TabBar(
               tabs: _tabs.map((e) => e.tab).toList(),
@@ -101,7 +101,7 @@ class _AuthorizedGroupPageScreenState
           Expanded(
             child: TabBarView(
               controller: _tabController,
-              children: _tabs.map((e) => e.widget).toList(),
+              children: _tabs.map((e) => e.widget(context)).toList(),
             ),
           ),
         ],
@@ -172,7 +172,7 @@ class _AuthorizedGroupPageScreenState
 }
 
 class _GroupPageTab {
-  final Widget widget;
+  final WidgetBuilder widget;
   final String label;
 
   const _GroupPageTab({