Update navigation logic and styling for a shopify theme

We have a shopify theme 'Empire' (https://themes.shopify.com/themes/empire/styles/supply)

The ability to set mega menus is limited to 5 in the navigation. We need this limit increased to unlimited.
Screen shot - https://tinyurl.com/2ef4rh8h


Additionally
We need the menu in desktop view to stop hiding on scroll as explained in this video
https://www.awesomescreenshot.com/video/13092665?key=e616ab9f4619aa18e10b29b7e03b619f


Site Access
https://uorganic-uk.myshopify.com/
password : antosi