[Gtk-3.18] Provide gap between buttons in message dialog. Fixes #498

Author: khurshid-alam

gtk-3.0/scss/widgets/_misc.scss

@@ -38,9 +38,9 @@
 
 @include exports("dialogs") {
     GtkMessageDialog, .message-dialog, .prompt {
-        -GtkDialog-content-area-border: 0;
+        -GtkDialog-content-area-border: $spacing;
         -GtkDialog-action-area-border: $spacing;
-        -GtkDialog-button-spacing: 0;
+        -GtkDialog-button-spacing: $spacing;
 
         margin: 0;
         padding: 0;