Hi There,
Currently, there are two css rules that giving the topbar a position: fixed;
property

You can add the .no-touchevents
class on the css selector to make it desktop specific and don’t affect the mobile.
.no-touchevents .masthead.masthead-inline .x-topbar {
position: fixed;
top: 0;
right: 0;
left: 0;
z-index: 2000;
}
I think there is no need for the second css rule. Please remove that.
Hope it helps, Cheers!