Header Background Image

Site URL: https://finemik.squarespace.com/

Hello.
I am trying to add an image as a background for my header.
I have tried the following code:
 

.header-announcement-bar-wrapper {
  background-image:url('url goes here'); 
  background-repeat:no-repeat; 
  background-size:cover;
  background-position: center;
} 
.header {
  background-color:rgba(0,0,0,0)!important
}

But it does nothing..
I also have a "scroll-to-top" function using an image, and was wondering if that could cause any problems..
I really need some help here.

Your site is private. Can you setup password & share url again?