functions.php

add_filter( 'body_class', 'knx_body_class_for_pages' );
/**
 * Adds a css class to the body element
 *
 * @param  array $classes the current body classes
 * @return array $classes modified classes
 */
function knx_body_class_for_pages( $classes ) {
	global $post;
	$classes[] = $post->post_name;
	return $classes;
}