Having trouble adding my plugin css

Can someone please help me with my code to load my plugin CSS.

Abstract: I am writing a plugin and want to apply styles to my admin pages. I have created a css file in my plugin directory and am trying to load it with the code below. The style is not being loaded


add_action( 'wp_enqueue_scripts', 'nst_admin_styles' );

function nst_admin_styles() {
$nstplugindir = plugins_url('nexus-ticker/nst-css.css');
wp_register_style('nst-css', $nstplugindir, array());
wp_enqueue_style( 'nst-css');
}

Thanks for you help,

Craig