responsive mobile menu with submenu help (website says Forbidden access)

Hi all, I don’t believe this falls under “programming” so I’m posting it in Uncategorized. Hopefully that’s OK.

I was wondering if anyone could help with this js created by Sergio Vitov. The original website keeps giving me a Forbidden access error. A poster has pasted the css, js, & html here:

I don’t really know javascript, but was wondering if there’s a simple way to add a submenu for the menu options (responsive, too), or if the author added that option & I’m missing that… Thanks in advance.