Can anyone help why my design is not working correctly?

I’ve created a theme using the base code: It works lovely except when the page is resized to a small size mobile phone size). The nav bar resizes as expected but the links don’t show at all. I’m not sure where the code mis o the page to check. AS the code is used on a SharePoint 2019 on prem site, I’ve had to strip out the forms as we couldn’t import the code with the tags.

I’ve also had to include all the CSS etc in the same file to ensure it works for all staff who might not have access to certain parts of our environment. Unfortunately I cant paste all the code into this window :frowning: