Hi Bodhu,
First of all, we do apologize that we did not give you a context regarding the support for this kind of customization. Let me give you detailed information:
The problem that you are experiencing is because you try to achieve a feature that theme does not support. Our theme does not have a feature to extend the mobile menu to bigger screen sizes. You need to remove the customization. I removed the Custom CSS from X > Theme Options > CSS and the original view showed:

The problem that I see in that case is that you set the link color to white and it does not show the menu items there. You need to go to X > Theme Options > Header > Navbar Link and change the color from white to something that shows the links correctly:

Now it seems that the whole reason you want to extend the mobile menu to the larger screen sizes is that the menu goes to two lines. You can fix that by changing the font size of the menu items by adding the CS code below to X > Theme Options > CSS:
body.x-navbar-fixed-top-active .x-navbar .desktop .x-nav>li>a>span {
font-size: 14px;
padding-left: 10px;
padding-right: 10px;
}
body.x-navbar-fixed-top-active .x-navbar .desktop .x-nav>li>a {
padding-left: 5px;
padding-right: 5px;
}
@media (max-width: 1256px) {
body.x-navbar-fixed-top-active .x-navbar .desktop .x-nav>li>a>span {
font-size: 13px;
}
}
Please kindly do not try to expand the mobile menu to larger screens as it is not only a matter of CSS and the Javascript complicated stuff is also involved which you will not be able to customize easily and such customization is outside of our support scope.
Thank you for your understanding.