how add magic action box form with CSS the other site?

For example. I use sumome (http://sumome.com)
Custom Form (sumome)
Paste in an HTML form to completely customize your popup. You should include a complete form that collects emails off-site using a service such as AWeber, MailChimp, or Campaign Monitor. Your service should be configured to redirect back to your site.
from sumome FAQ
Can I customize the look and feel of the popup?

You can use our default options or fully control the CSS in the advanced section.
I use this:

<link rel="stylesheet" type="text/css" href="http://mysite.com/wp-content/plugins/magic-action-box/styles/royalty/style.css">     

<form action="http://mysite.com/?wpmlmethod=offsite&title=%D0%91%D1%8B%D1%81%D1%82%D1%80%D0%B0%D1%8F+%D1%81%D0%B8%D1%81%D1%82%D0%B5%D0%BC%D0%B0&list=3" method="post">
<input type="hidden" name="list_id[]" value="3" />
<div class="mab-field">
<label for="wpml-1456527139email"></span></label> <input id="wpml-1456527139email" type="text" name="email" placeholder="Ваш Email"/>
</div>
<div class="mab-field">
<input type="submit" name="subscribe" class="mab-optin-submit" value="Подписаться" />
</div>
<div class="clear"></div>
</form>

All ok, but CSS not work.
Is it my error?

https://wordpress.org/plugins/magic-action-box/