Adds the current editing post's ID to body_class in WordPress admin

post_id_body_class_wp_admin.txt

// Adds the current editing post's ID to body_class in WordPress admin
// Add this code in your theme's funtions.php
function post_id_to_body_admin($pid) {
	$screen = get_current_screen();
    if ( 'post' == $screen->base ) {
		global $post;
		$pid .= ' post-id-' . $post->ID;
		return $pid;
	}
}
add_filter('admin_body_class', 'post_id_to_body_admin');