Quick js and/or css fix

Hi there,
I have a website with a responsive hambuger menu combined with a sticky header, which doesn't show up all the navigation items on mobile view due to the fact that the menu does not fit into the screen. I need to be able to scroll and see all navigation items when the menu is expanded and still have the sticky header when collapsed.
I can send over the files to work with.

Navigation: https://www.cssscript.com/demo/responsive-dropdown-animenu/
Sticky header: https://www.w3schools.com/howto/howto_js_sticky_header.asp

Thanks
Alessia