How can I make the menu bar responsive?

Hiya, I’m trying to use a plugin to make the custom menu bar responsive and move downwards in tandem with the infinite scroll function in this theme, however that’s not working. It can get tedious scrolling all the way back up to the custom menu for navigation. A shame to lose the menu bar right after a user clicks the ‘get start’ button. Any idea how I can fix that? Thanks x