Mobile header on landing page is not responding. How do I fix?

Hello,

Here is the page: http://go.rwc.com/IBS-2020.html 

This is a coded template from a previous agency my team used. The landing page looks good, except when in mobile only because of the header not responding correctly. I'm not sure how to fix within the template code. Any suggestions? I am not proficient in CSS  

Thanks!

#landing page issue‌ #html css for marketo‌