Hemingway mobile menu- Make nested

Hey guys,

Forgive me if this has been posted before but I have not come across it in my searches…

I absolutely love the Hemingway theme and have fumbled my way through some customisation (I have very limited knowledge in HTML, CSS & PHP) to get it to pretty well my ideal site. The final adjustment I would like to make it to make the mobile menu ‘nested’ (if that’s the correct term). Much like the full screen main menu, when the mobile menu is selected I would like only to see the top level menu options with a ‘drop down’ arrow to let users know there are child menu options.

I hope this all makes sense, my website is headforthehills.net.au.

Cheers- Tyson