Hi there,
you can add this PHP Snippet:
add_filter('body_class','add_category_to_single');
function add_category_to_single($classes) {
if (is_single() ) {
global $post;
foreach((get_the_category($post->ID)) as $category) {
// add category slug to the $classes array
$classes[] = $category->category_nicename;
}
}
// return the $classes array
return $classes;
}
https://docs.generatepress.com/article/adding-php/
this will add the category slug to the single post body. You can then target it with CSS like so (add appropriate category slug):
.single-post.category-slug {
CSS Rules here
}