Unable to open sub-menus on the mobile version

Hi,
I just set up my WordPress website with your theme “Density” and love it!
Thank you for the awesome design.

But on mobile size, the sub-menus doesn’t open. It works properly on Desktop version.
It just doesn’t work. Even I did not edit any code of it.
Also, I would appreciate if you can let me know how to add other icons on the social bar (the black one).

Thank you!