osd: Restyle OSD display popup

- remove class from label box
- new style for label itself

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2277>

data/theme/gnome-shell-sass/widgets/_osd.scss

@@ -14,8 +14,6 @@ $osd_levelbar_height:6px;
 
   StIcon { icon-size:$large_icon_size;}
 
-  .osd-monitor-label { font-size: 3em; }
-  
   StLabel {
     &:ltr { margin-right: 6px; }
     &:rtl { margin-left: 6px; }
@@ -37,6 +35,17 @@ $osd_levelbar_height:6px;
   }
 }
 
+// Monitor number label
+.osd-monitor-label { 
+  @extend %osd_panel;
+  border-radius: $modal_radius;
+  font-size: 3em;
+  font-weight: bold;
+  margin: $base_margin * 3;
+  text-align: center;
+  min-width: 1.3em;
+}
+
 /* Pad OSD */
 .pad-osd-window {
   padding: 32px;

js/ui/osdMonitorLabeler.js

@@ -13,7 +13,6 @@ class OsdMonitorLabel extends St.Widget {
         this._monitor = monitor;
 
         this._box = new St.BoxLayout({
-            style_class: 'osd-window',
             vertical: true,
         });
         this.add_actor(this._box);