design: Minor design refactoring

lib/views/ui/chat_ui.dart

@@ -511,7 +511,7 @@ class ChatUI extends StatelessWidget {
                         controller.room.membership == Membership.join
                     ? Container(
                         decoration: BoxDecoration(
-                          color: Theme.of(context).backgroundColor,
+                          color: Theme.of(context).scaffoldBackgroundColor,
                         ),
                         child: Row(
                           crossAxisAlignment: CrossAxisAlignment.end,

lib/views/ui/settings_ui.dart

@@ -38,13 +38,7 @@ class SettingsUI extends StatelessWidget {
             expandedHeight: 300.0,
             floating: true,
             pinned: true,
-            title: Text(L10n.of(context).settings,
-                style: TextStyle(
-                    color: Theme.of(context)
-                        .appBarTheme
-                        .textTheme
-                        .headline6
-                        .color)),
+            title: Text(L10n.of(context).settings),
             actions: [
               FutureBuilder(
                   future: controller.crossSigningCachedFuture,

lib/views/widgets/list_items/message.dart

@@ -258,7 +258,7 @@ class _MetaRow extends StatelessWidget {
         Text(
           event.originServerTs.localizedTime(context),
           style: TextStyle(
-            color: color.withAlpha(164),
+            color: color.withAlpha(180),
             fontSize: 10 * AppConfig.fontSizeFactor,
           ),
         ),