Register custom widget class definition files and custom widget category.

elementor-customization-init.php

<?php

// Load the theme's custom Widgets so that they appear in the Elementor element panel.
add_action( 'elementor/widgets/widgets_registered', 'register_elementor_widgets' );
function register_elementor_widgets() {
	// We check if the Elementor plugin has been installed / activated.
	if ( defined( 'ELEMENTOR_PATH' ) && class_exists('Elementor\Widget_Base') ) {
		require_once( get_template_directory() . '/widgets/course-box.php' );
		require_once( get_template_directory() . '/widgets/h2-content.php' );
		require_once( get_template_directory() . '/widgets/h3-content.php' );
		require_once( get_template_directory() . '/widgets/program-requirement.php' );
		require_once( get_template_directory() . '/widgets/schedule.php' );
 	}
}

// Add a custom 'mld' category for to the Elementor element panel so that 
// our theme's widgets have their own category.
add_action( 'elementor/init', function() {
	\Elementor\Plugin::$instance->elements_manager->add_category( 
		'mld',
		[
			'title' => __( 'MLD', 'mld' ),
			'icon' => 'fa fa-plug', //default icon
		],
		1 // position
	);
});