entronauten on "[Plugin: Contact Form 7] Checkboxes does not appear in Safari"

I set up a few checkboxes in my form and it works fine in firefox, but for some reason the checkboxes aren't appearing in Safari. What can I do? I saw that a similar topic was resolved, but it doesn't help me.
The URL is:
http://www.alinakirschniok.de/cms/seminar-achtsamkeit-und-stressbewaeltigung/

Thanks and have a nice weekend!

Chris

http://wordpress.org/extend/plugins/contact-form-7/