We are having the same issue on our sites.
I added this code. In the inspector on my desktop it seems to work, but I can’t get it to work on my mobile device (iPhone or Samsung).
I am using the Beaver Builder theme.
Link: http://www.inception-example21.com/
Yes, that worked. They are still kind of indented far, but definitely better.
However, I don’t see third level menu items.
Example site: http://www.dental.inceptionimages.com/design-1/
Under “Services” tab, there are four services and then each service has additional items under it. Those additional items don’t show up on the mobile menu.