How to change the layout of the mobile version of a Big Cartel website

I'm setting up a new website using Big Cartel, and the mobile version for my theme doesn't display the page links I have in my site header! It only wants to display them if I put them in the site footer, which I don't want to do.

I have tried to display my page links through the site footer, which works, but isn't what I'm looking to do. I have contacted Big Cartel for support, and basically what they told me is that it'd take a fair bit of digging into the CSS code and I should try posting it to Stackoverflow. I know it says not to post the entire CSS code, but I don't really know what else I could show you because I am entirely lost as far as how to make my page links show up in the site header on my mobile website. So I have attached a pastebin link to it, and then a little bit of code because Stackoverflow won't let me post my question unless I attach a little code.

https://pastebin.com/RLLmCjES

#site_header {
position: fixed;
top: 0;
z-index: 10;
width: 100%;
padding: 25px 0;
}