How to keep navigation bar on one line on different devices

Site URL: https://venturatherapycollective.squarespace.com/

Hello!

I am just about done with a website for client, but she's still saying that the navigation bar splits into two lines on her computer. I explained to her that depending on the size of the screen the website can auto adjust to fit, but i'm sure there is a code I can add to minimize the chances of that happening. 

I've tried other codes and nothing has seemed to work yet. Curious if anyone has a good code they like to use on sites that can help with this common problem? 

Thank you!

Password: Ventura

Add to Design > Custom CSS

nav.header-nav-list {
    flex-wrap: nowrap !important;
}