Ultraschall is a enhanced-modification of Reaper, optimized for podcaster's workflows.
In the screenshot, you can see the Reaper's main toolbar underneath the Ultraschall-logo which emplys such gaps.
Such gaps between buttons can be added using the menu-editor.
Have a look at the user-manual that you can download from here for how to do it:
https://www.reaper.fm/userguide.php