ui fixes

example/lib/group_chat_details_screen.dart

@@ -61,6 +61,7 @@ class _GroupChatDetailsScreenState extends State<GroupChatDetailsScreen> {
       child: Scaffold(
         backgroundColor: StreamChatTheme.of(context).colorTheme.whiteSnow,
         appBar: AppBar(
+          brightness: Theme.of(context).brightness,
           elevation: 1,
           backgroundColor: StreamChatTheme.of(context).colorTheme.white,
           leading: const StreamBackButton(),

example/lib/new_chat_screen.dart

@@ -121,6 +121,7 @@ class _NewChatScreenState extends State<NewChatScreen> {
     return Scaffold(
       backgroundColor: StreamChatTheme.of(context).colorTheme.whiteSnow,
       appBar: AppBar(
+        brightness: Theme.of(context).brightness,
         elevation: 0,
         backgroundColor: StreamChatTheme.of(context).colorTheme.white,
         leading: const StreamBackButton(),

example/lib/new_group_chat_screen.dart

@@ -50,14 +50,15 @@ class _NewGroupChatScreenState extends State<NewGroupChatScreen> {
 
   @override
   Widget build(BuildContext context) {
-    return SafeArea(
-      child: Scaffold(
-        backgroundColor: StreamChatTheme.of(context).colorTheme.whiteSnow,
-        body: NestedScrollView(
+    return Scaffold(
+      backgroundColor: StreamChatTheme.of(context).colorTheme.whiteSnow,
+      body: SafeArea(
+        child: NestedScrollView(
           floatHeaderSlivers: true,
           headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
             return <Widget>[
               SliverAppBar(
+                brightness: Theme.of(context).brightness,
                 pinned: true,
                 forceElevated: true,
                 elevation: 1,