Change responsiveness threshholds for primary menu

Hello - I'm developing a site for a client using Catch Base. The primary menu has only a few items, and the client would prefer it if it was still visible on narrower layouts, without the mobile menu icon replacing things until a narrower threshhold. Is this something we can customize (I'm not afraid to dig into the .js or .css , just need pointers on what to look for.) Thanks in advance for any suggestions.