fix a coding issue on mobile navigation

I have a simple javascript / css hamburger menu (https://kastt.uk/dev2/store.html) that opens links in an iframe, everything works well on desktop & also tablet size screens, but because the links are opening in an iframe the slide in menu does not close after a link is clicked. Which makes the navigation unuseable on smaller handheld devices as it's covering the page content until the X is clicked.

Please don't ask for server access because I can't provide that, but I can send html, css etc
I've researched and tried most of the online solutions - but I don't know enough JS to get any of it to work. Thanks