Tutorial Add Category Name to body_class
The body_class function is nice for adding a bunch of classes to the body tag that have information about what kind of page is currently being displayed. Probably for styling purposes. But for whatever reason, it doesn't include a class for the current category (or categories) for a single post.
This adds that category "nice" name:
add_filter('body_class','add_category_to_single');
function add_category_to_single($classes, $class) {
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;
}