Changing Mobile Navigation Responsive Breakpoint

If you want to change the mobile navigation responsive breakpoint, in order to show the mobile navigation earlier, add the following CSS code into Appearance » Customize » Additional CSS:

@media handheld, only screen and (max-width: 1200px) {
    #main-nav {
        display: none !important;
    }
}

@media handheld, only screen and (max-width: 1200px) {
    #show-nav-menu {
        display: inline-block;
    }
}

1200px is the width when regular navigation gets hidden and mobile navigation shows up. Feel free to change it as needed.