too much menu items (mainmenu getting to long) – need hamburger menu faster

hello,

i love the theme zerif lite.
but i have a problem with my mainmenu.
i have many items – so the menu getting relative long.

between the width 767 and 992 – i need to have the hamburger menu.
at the moment the normal horizontal mainmenu is just centered direct under the logo.

another question:
is there ans possibilty to make the hamburger menu sticky (inluding the logo and the background)?

best regards