Show navigation menu as text - not dropdown menu?

Hello all.

How do I have the navigation menu, the nav menu are just links, as text and not dropdown menu (2 lines)?

The url is: https://www.keflaviktransfer.com/

Thanks!

This code by @tuanphan kinda does it but the font size is to big on the navigation.

@media screen and (max-width:767px) {
.header-display-desktop {
    display: flex !important;
}
.header-display-mobile {
    display: none !important;
}
.header-burger {
    display: none;
}
.header-title-nav-wrapper {
    flex: 1 0 100% !important;
}
.header-nav {
    display: flex !important;
    width: 70% !important;
    flex: 1 1 70% !important;
}
.header-title {
    flex: 1 0 30% !important;
}
}