How to add line to bottom of header on mobile [SS7.0 / Brine]

Site URL: https://brshadley-sporting-report.com/

Hello, thanks in advance for any help. I'd like to a line to the bottom of my fixed header on mobile. Squarespace 7.0, Brine template. 

I was able to achieve this on desktop (code: .Header { border-bottom: 2px solid #ffc330; }), but it doesn't transfer to mobile and I haven't been able to find any code that works on mobile. Any help appreciated. 

Ben

Use this code

.Mobile-bar.Mobile-bar--top {
    border-bottom: 2px solid #ffc330;
}