Merge branch 'wip/jimmac/suggested-destructive-focus' into 'master'

Adwaita: suggested destrictive button focus

Closes #2704

See merge request GNOME/gtk!1841

gtk/theme/Adwaita/_common.scss

@@ -676,6 +676,7 @@ button {
                              (destructive-action, $destructive_color) {
     &.#{$b_type} {
       @include button(normal, $b_color, white);
+      @include focus-ring($fc: transparentize(white,0.1));
 
       &.flat {
         @include button(undecorated);