Nested submenus

Hi guys,

I have just spotted a significant flaw in your theme. I want to display nested submenus. However, it looks like there is no styling included to correctly present the navigation menu hierarchy.
The theme works fine if the menu is only one level deep. It fails if I would like to add more subcategories (i.e. ‘Home’>’Category’ looks fine; ‘Home’>’Category’>’Subcategory’>’Subcategory’ does not display links correctly.
Is it something I can improve by tweaking theme settings in customiser (I did not find any related options)?
Or you recommend to build it up on my own in CSS styles?

Kind Regards