design: iOS related adjustments for onboarding

lib/pages/homeserver_picker/homeserver_picker_view.dart

@@ -143,7 +143,10 @@ class HomeserverPickerView extends StatelessWidget {
                                       const EdgeInsets.symmetric(vertical: 12),
                                 ),
                                 onPressed: controller.restoreBackup,
-                                child: Text(L10n.of(context)!.hydrate),
+                                child: Text(
+                                  L10n.of(context)!.hydrate,
+                                  textAlign: TextAlign.center,
+                                ),
                               ),
                             ),
                           ),

lib/widgets/layouts/login_scaffold.dart

@@ -22,7 +22,6 @@ class LoginScaffold extends StatelessWidget {
     final isMobileMode = !FluffyThemes.isColumnMode(context);
     final scaffold = Scaffold(
       key: const Key('LoginScaffold'),
-      backgroundColor: isMobileMode ? null : Colors.transparent,
       appBar: appBar == null
           ? null
           : AppBar(
@@ -51,7 +50,7 @@ class LoginScaffold extends StatelessWidget {
     if (isMobileMode) return scaffold;
     return Container(
       decoration: BoxDecoration(
-        gradient: FluffyThemes.backgroundGradient(context, 156),
+        gradient: FluffyThemes.backgroundGradient(context, 255),
       ),
       child: Column(
         children: [