wp_enqueue_style not working when using get_stylesheet_directory_uri()

I'm trying to enqueue a stylesheet in my Wordpress child theme:

function as_scripts() {
  wp_enqueue_script( 'custom-script', get_stylesheet_directory_uri() . '/js/as-script.js', array( 'jquery' ), '', true );
  wp_enqueue_script( 'slick-script-2', '//code.jquery.com/jquery-1.11.0.min.js' );
  wp_enqueue_script( 'slick-script-3', '//code.jquery.com/jquery-migrate-1.2.1.min.js' );
  wp_enqueue_script( 'slick-script', get_stylesheet_directory_uri() . '/slick/slick.min.js' );
  wp_enqueue_style(  'slick-css', get_stylesheet_directory_uri() . '/slick/slick.css' );
}

add_action( 'wp_enqueue_scripts', 'as_scripts', 99 );

All of the scripts are enqueued properly except for the stylesheet. When I try to use get_template_directory_uri(), the stylesheet is loaded, but obviously not found because is not in the parent theme, but in the child theme. I also tried typing the absolute path to the file, but it's not loaded on the page either.

Any help appreciated.