Create WP dashicon for Custom Post Type within a class

gistfile1.php

<?php
class CLASSNAME {
	public function __construct() {
			add_action( 'admin_head', array($this, 'classname_add_menu_icons_styles') );
	}
	public static function classname_add_menu_icons_styles() {
	  	?>
	  		<style>
	  		#adminmenu .menu-icon-post_type div.wp-menu-image:before {
	  		  content: "\f323";
	  		}
	  		</style>
	  	<?php
	}
}
$classname = new CLASSNAME();
?>