GTK 3.22: Fixes #634

src/gtk-3.20/scss/apps/_gnome-applications.scss

@@ -29,3 +29,31 @@
         }
     }
 }
+
+
+/************************
+ ! Unity-Control-Center *
+*************************/
+
+@include exports("unity-control-center") {
+    // Fixed: https://github.com/numixproject/numix-gtk-theme/issues/634
+    .background:not(.csd):not(.solid-csd) > box.vertical > notebook.frame {
+        // hide unwanted frames
+        border: 0 none transparent;
+
+        > stack > scrolledwindow > viewport > box.vertical > frame > box.vertical {
+            // reset $base_color;
+            iconview.view {
+                &, &:backdrop {
+                    background-color: transparent;
+                }
+
+                &:selected {
+                    &:focus, & {
+                        @extend %selected_items;
+                    }
+                }
+            }
+        }
+    }
+}