WordPress Customizer Additional CSS – line numbers overlaps CSS code

Instead of doing it that way I found a code snippet to add a new css file. Here is the new code:

function add_my_customizer_styles() {
wp_enqueue_style( 'my-customizer-css', trailingslashit( get_stylesheet_directory_uri() ).'assets/styles/customizer.css', null );
}
add_action( 'customize_controls_print_styles', 'add_my_customizer_styles', 99 );

That is working fine. Evidently, while the previous code works for some areas of the admin it didn’t work for the Customizer. This way I was able to make the customizer wider, too, which I’ve always wanted to do, by adding this additional CSS:

.wp-full-overlay-sidebar { width: 400px; }
.wp-full-overlay.expanded {margin-left: 400px; } 

Problem solved!