How to change style of sticky menu

I want to edit the style that the menu appears as once it has been stuck to the top of the page so that it matches the look of the normal menu when the page has not been scrolled down. How can I go about doing this?

I am fairly new to wordpress and I am currently experimenting with the features on offer so any advice would be greatly appreciated!

Thanks!

https://wordpress.org/plugins/sticky-header/