Can't change Mobile Menu appearance

Hi everyone, 

I have been trying to change my mobile menu for the past hour or so with no luck. Have gone through a bunch of tutorials and it seems like no matter what I try I cannot change the appearance of my mobile menu at all. 

I want the menu to overlay the whole page and change the spacing between options, but that doesn't seem to be possible. I'm using the beautiful WELLS template which has a sidebar, which might be causing the issue? 

When I try to search for 'menu' in site styles nothing shows up. I have attached some images as reference, please let me know what is causing this! 

Website is: arsalanmotavali.com

Password: test

Thanks! 

I have just tried to preview another template, which gives me the menu options back. Perhaps it is a template restriction, which is frustrating as I love this look. Are there any workarounds? 

@arsalanpeto It might not solve it completely, but this should help.

Go to Website -> Website Tools -> Custom CSS and paste this -

.menu-open {
height: 94vh !important;
align-content: center !important;
}

@JessicaM definitely helps, thanks! still frustrating to not have the full suite of customisation built-in to the template, which is strange, but this is looking much better on mobile at least. thanks!