chore: Follow up design

lib/pages/chat/chat_view.dart

@@ -256,6 +256,8 @@ class ChatView extends StatelessWidget {
                         onPressed: controller.scrollDown,
                         heroTag: null,
                         mini: true,
+                        backgroundColor: theme.colorScheme.surface,
+                        foregroundColor: theme.colorScheme.onSurface,
                         child: const Icon(Icons.arrow_downward_outlined),
                       ),
                     )

lib/pages/chat/events/message.dart

@@ -184,13 +184,10 @@ class Message extends StatelessWidget {
                         child: Material(
                           borderRadius:
                               BorderRadius.circular(AppConfig.borderRadius / 2),
-                          color: selected
+                          color: selected || highlightMarker
                               ? theme.colorScheme.secondaryContainer
-                                  .withAlpha(100)
-                              : highlightMarker
-                                  ? theme.colorScheme.tertiaryContainer
-                                      .withAlpha(100)
-                                  : Colors.transparent,
+                                  .withAlpha(128)
+                              : Colors.transparent,
                         ),
                       ),
                     ),