Deprecated functions

I am not a coder but the commented lines below don't work anymore.
I managed to get it to work but once again i am not a coder so if you could look at it so the module work, thanks

FullScreenModeBlock.php
//$css_path = drupal_get_path('module', 'full_screen_mode') . '/css/full-screen-mode.css';
$css_path = base_path() . \Drupal::service('extension.list.module')->getPathname('full_screen_mode') . '/css/full-screen-mode.css';

//$css_url = file_create_url($css_path);
$css_url = \Drupal::service('file_url_generator')->generateAbsoluteString($css_path);
$build['#attached']['drupalSettings']['css_url'] = $css_url;
$build['#attached']['library'][] = 'full_screen_mode/full_screen_mode';