Issue with fly out menu

I’ve taken over a site that is using a custom menu. It’s working fine, but when you hover over a link to get the fly out, it comes flying in from the edge of the browser instead of just displaying neatly alongside.

The site URL is: https://caarc.php.wired.co.nz/ (login:wired/wired)

The CSS is: https://pastebin.com/d1BmYB4g

And the HTML is: https://pastebin.com/ZdmZHFVK

I would like the fly out to behave in a “normal” manner and not wildly fly in from the edge of the browser.

Also, I would ideally like to make the page list dynamic, so if anyone can advise how I can use the existing styles in <?php wp_list_pages(); ?> (or <?php wp_nav_menu(); ?>) that would be awesome!

I’m a bit confused with this and any help offered would be greatly appreciated! Thank you