Fix colors and make passphrase submittable via Enter

With this change, the lobby selector gets its dark background back.
Also, now the passphrase can be submitted by pressing Enter and not only
by clicking the 'check' icon.

lib/pages/lobby_selector.dart

@@ -61,6 +61,7 @@ class _LobbySelectorState extends State<LobbySelector> {
       context: context,
       builder: (BuildContext context) {
         return Scaffold(
+          backgroundColor: Colors.transparent,
           body: AlertDialog(
             title: const Text('Host or join?'),
             actions: <Widget>[
@@ -100,18 +101,14 @@ class _LobbySelectorState extends State<LobbySelector> {
                 title: const Text('Enter the passphrase here:'),
                 content: TextField(
                   controller: phraseController,
+                  onSubmitted: (val) {
+                    submitPassphrase(builderContext);
+                  },
                   decoration: InputDecoration(
                       hintText: 'Enter passphrase here',
                       suffixIcon: IconButton(
                         onPressed: () {
-                          joinGameFuture = joinPrivateGame(builderContext);
+                          submitPassphrase(builderContext);
-                          joinGameFuture.then((value) {
-                            if (value != null) {
-                              phraseController.clear();
-                              builderContext.pop();
-                              switchToGame(value);
-                            }
-                          });
                         },
                         icon: const Icon(Icons.check),
                       )),
@@ -132,6 +129,17 @@ class _LobbySelectorState extends State<LobbySelector> {
     );
   }
 
+  void submitPassphrase(BuildContext ctx) {
+    joinGameFuture = joinPrivateGame(ctx);
+    joinGameFuture.then((value) {
+      if (value != null) {
+        phraseController.clear();
+        ctx.pop();
+        switchToGame(value);
+      }
+    });
+  }
+
   void switchToGame(PlayerInfo info) {
     var chessGameArgs = ChessGameArguments(
         lobbyID: info.lobbyID!,