Black background Header for Blog posts

Site URL: https://guitar-ray-t57a.squarespace.com

Hi, 

Trying to get a black BG for every blog post. Used some of the recommended coding found on other threads with similar topic.... no success...

.collection-type-blog-basic-grid.view-item header#header {
    background: black;
  	
}

any thoughts ?

site: https://guitar-ray-t57a.squarespace.com 

example post: https://guitar-ray-t57a.squarespace.com/news/blog-post-title-one-mt27n

thanks !

Arno