Nícholas André

Here is the problem:

public function enqueue_requeried_scripts(){
396	                wp_enqueue_style("jquery-ui-style");
397	                wp_enqueue_script("jquery-ui-slider");
398	        }

You are enqueue your registered style in every single admin page. You should check and do this only on you admin page.

The problem is in Admin Panel. The plugin is enqueue the jquery-ui styles and overriding the default WordPress jQuery UI styles. You should only enqueue on the admin page of WP Lightbox 2.