Fix swaync fullscreen background by raising CSS priority to user level

libadwaita overrides application-level CSS, causing a visible
background behind the control center overlay. Setting cssPriority
to "user" ensures custom styles take precedence.

defaults/xdg/swaync/config.json

@@ -5,7 +5,7 @@
     "positionY": "top",
     "layer": "overlay",
     "control-center-layer": "top",
-    "cssPriority": "application",
+    "cssPriority": "user",
 
     "notification-window-width": 300,
     "notification-icon-size": 64,