Adwaita: fix outline for scale trough

gtk/theme/Adwaita/_common.scss

@@ -2504,7 +2504,12 @@ scale {
   }
 
   // the backing bit
-  trough { @extend %scale_trough; }
+  trough {
+    @extend %scale_trough;
+
+    outline-offset: 2px;
+    -gtk-outline-radius: 4px;
+  }
 
   // the colored part of the backing bit
   highlight { @extend %scale_highlight; }

gtk/theme/Adwaita/gtk-contained-dark.css

@@ -2658,6 +2658,9 @@ scale {
     margin: -8px; }
   scale.fine-tune slider {
     margin: -6px; }
+  scale trough {
+    outline-offset: 2px;
+    -gtk-outline-radius: 4px; }
   scale fill, scale fill:backdrop {
     background-color: #1c1f1f;
     box-shadow: none; }

gtk/theme/Adwaita/gtk-contained.css

@@ -2689,6 +2689,9 @@ scale {
     margin: -8px; }
   scale.fine-tune slider {
     margin: -6px; }
+  scale trough {
+    outline-offset: 2px;
+    -gtk-outline-radius: 4px; }
   scale fill, scale fill:backdrop {
     background-color: #9d9d99;
     box-shadow: none; }