Hi Daniel.
Thank you for your honest answer. I can live with this solution, that I never would have found out alone. I very much appreciate your support.
Just to help you understand, why I asked for a possible code change in the former post: When I create the menu for a WP-site, my backend looks like this: 
.
With every theme I’ve used before, the corresponding menu would look like this: Example 1 “Twenty Fourteen”
Example 2 – one of yours, Pinboard
But now, example 3 – Enlightenment
Can you imagine, why the look of number 3 confused me? I hadn’t done anything different from what I did in the past. Just add pages to the menu, move a few of them a step to the right (for sub-menu-items) and that’s it. With your help I found out how to make the menu look with the enlightenment theme as desired. But it was not the way I expected to achieve this look. Learned something new today.
Once again thank you for your help.
Best regards,
Christian