Custom styles for PopUp Pro from WPMU Dev

add_placeholder.js

jQuery('document').ready(function($){
	
	$('input[name=subscription-email]').attr('placeholder','Enter your email address...');	

});

animate_popup.css

.has-popup .wdpu-msg {
  -webkit-animation-name: bounceInDown;
          animation-name: bounceInDown;
  -webkit-animation-duration: 2s;
          animation-duration: 2s;                   
}

custom_popup_styles.php

function my_custom_popup_styles( $list ) {
	$list[] = (object) array(
		'url' => get_template_directory_uri() . '/popup-custom-styles-master/elegant/',
		'dir' => get_template_directory() . '/popup-custom-styles-master/elegant/',
		'name' => 'Elegant',
	);

	return $list;
}

add_filter( 'popup-styles', 'my_custom_popup_styles' );