Fixed header on tablet?

I have a responsive site with a fixed header (sticky) and it is working fine.
But when the screen is less than 980 px, it is not longer fixed.
I want to fix the header from 350px or so.
You can see the site to see what I mean: http://www.bernadettegoossens.nl/1456-2/

How to manage that?

Thanks

Hi There,

Please add the following CSS under Customizer > Custom > Global CSS:

@media (max-width: 979px){
    .x-navbar.x-navbar-fixed-top {
        position: fixed;
    }
}