CSS for Mobile Navigation

I’m using Canvas for my website and primary-menu, style-2 class for the navigation. I’ve been able to customize the CSS for the menu when it’s on a device larger than a tablet, but I haven’t been able to find the CSS for when it’s on a mobile device. I’d like to change the font and color. I’ve looked through style.css, bootstrap.css and responsive.css, but haven’t located it. Can anyone direct me to where it is? Many thanks!