Hello There,
Thanks for writing in! The default breakpoint is 980 pixels. Lower than 980 pixels, the mobile menu will appear.
At the moment, you have set the background color of the navbar into transparent. I would suggest that you set it to have a background color instead. And in your homepage, please edit your page back in Cornerstone and insert the following custom css in the settings tab, Settings > Custom CSS
.home .x-navbar,
.home .x-navbar .sub-menu {
background-color: transparent !important;
}
This is to make sure that in your homepage you will have a transparent navbar and in all other pages, it will have a background color.
Hope this helps. Please let us know how it goes.