lightbox showing too low

hallo,
I’m having some problem with the woocommerce light box, but it was working just fine until a few days ago.

so the problem is, if you go to product page, then click on one product picture, there should be the picture of the product poping out, and that picture use to show in the middle, but now for some reason is showing so low that you can’t see the whole picture.

can any body help me fix it?
thank you

my site is http://celinda-design.de/?post_type=product

https://wordpress.org/plugins/woocommerce/