not possible
possible with custom css, read this to get a little introduction, this does not cover your special case: http://laytheme.com/documentation.html#custom-css-styling
3:
hm interesting, it seems the height of the navbar is vw, i guess i chose this bc the menu type could also be in vw and so i though that would be a good idea.
Use
.navbar {
height: 10vh;
}
instead in lay options -> custom html & css -> custom css for desktop version