I believe you need to add __FILE__ to your plugin_url() function. It may not be calling the right location. It should look like this:

add_action( 'wp_enqueue_scripts', 'wpse_238154_register_plugin_styles' );

function wpse_238154_register_plugin_styles() {
    wp_enqueue_style( 'fh-plugin' , plugins_url( 'nf-plugin/includes/f-hide.css', __FILE__ ) );
}

I believe you need to add __FILE__ to your plugins_url() function. It may not be calling the right location. It should look like this:

add_action( 'wp_enqueue_scripts', 'wpse_238154_register_plugin_styles' );

function wpse_238154_register_plugin_styles() {
    wp_enqueue_style( 'fh-plugin' , plugins_url( 'nf-plugin/includes/f-hide.css', __FILE__ ) );
}