💄(front) enhance ui first shot

Based on recent sketches, we decided to implement the new ui. This is
a first shot, more will be coming next.

src/frontend/src/features/rooms/livekit/components/SidePanel.tsx

@@ -68,6 +68,7 @@ const StyledSidePanel = ({
     >
       <Button
         invisible
+        variant="greyscale"
         size="xs"
         onPress={onClose}
         aria-label={closeButtonTooltip}