how to add stylesheet to particular plugin only?

by

You can use get_current_screen() to check which page is being displayed now, and if it was your plugin’s page, enqueue the script.

However the easier way is to use the global variable, $pagenow:

if(( $pagenow == 'my-plugin.php' ) {
    wp_enqueue_style('my-style', 'URL-HERE' );    
}

In which my-plugin.php is the slug of your plugin screen’s URL, such as:

www.example.com/wp-admin/my-plugin.php