Reply To: Change header background for category or pages

[Tom]

WordPress doesn’t add the category class to the single posts (for some reason).

You can manually add the classes to your single posts using a function like this: https://wordpress.org/support/topic/modify-body_class-output-to-show-category-slug-for-single-posts?replies=11#post-1396482

As for pages, it’s very similar to the above:

body.page-id-xx {
     background-image: url('');
}