Preventing site default design being deleted.

app/controllers/admin/designs_controller.rb

@@ -94,7 +94,12 @@ class Admin::DesignsController < OrbitBackendController
 
   def destroy
     @design = Design.find(params[:id])
-    @design.destroy
+    if @site.design == @design
+      flash[:error] = "Failed! You can not delete a design that used by default "
+    else
+      @design.destroy
+      flash[:notice] = "Successfully deleted design."
+    end
     redirect_to admin_designs_url
   end