chore: Adjust bubble color in dark mode

lib/pages/chat/chat_view.dart

@@ -249,10 +249,7 @@ class ChatView extends StatelessWidget {
                                         Radius.circular(AppConfig.borderRadius),
                                   ),
                                   elevation: 4,
-                                  shadowColor: Theme.of(context)
-                                      .colorScheme
-                                      .onBackground
-                                      .withAlpha(64),
+                                  shadowColor: Colors.black.withAlpha(64),
                                   clipBehavior: Clip.hardEdge,
                                   color: Theme.of(context).brightness ==
                                           Brightness.light

lib/pages/chat/events/message.dart

@@ -70,7 +70,7 @@ class Message extends StatelessWidget {
     final alignment = ownMessage ? Alignment.topRight : Alignment.topLeft;
     var color = Theme.of(context).brightness == Brightness.light
         ? Colors.white
-        : Colors.black;
+        : Theme.of(context).colorScheme.surfaceVariant;
     final displayTime = event.type == EventTypes.RoomCreate ||
         nextEvent == null ||
         !event.originServerTs.sameEnvironment(nextEvent!.originServerTs);
@@ -174,8 +174,7 @@ class Message extends StatelessWidget {
               child: Material(
                 color: noBubble ? Colors.transparent : color,
                 elevation: event.type == EventTypes.Sticker ? 0 : 4,
-                shadowColor:
-                    Theme.of(context).colorScheme.onBackground.withAlpha(64),
+                shadowColor: Colors.black.withAlpha(64),
                 borderRadius: borderRadius,
                 clipBehavior: Clip.antiAlias,
                 child: InkWell(