mysterysolver

Thanks you

Ok i figured it out by adding this code in funtions.php

/**
 * Adds category classes to the array of body classes - in single post only.
 *
 */
function add_category_body_classes( $classes ) {

	if ( is_single() ) {
		global $post;
		$cats = get_the_category($post->ID);
		foreach( $cats as $cat ) {
		$classes[] = 'category-' . $cat->slug;
		}
	}

	return $classes;
}
add_filter( 'body_class', 'add_category_body_classes' );

now i like to make the header images responsive , any idea ?

what do you mean by html image ?
can you show me a example ?