Jqzoom appears behind sidebar

[StSt]

Hello,

 

We run a prestashop v1.5.6.0, with a customised leo converse theme. I try to get the Jqzoom-function to work on product images. But when I activate it, the zooming-box appears behind the right sidebar with our categories. I can just see a slight stroke of the zooming-box so I know it's working, but it should be on top. Can anyone help us out?

 

I allready tried to change the z-index in js/jquery/plugins/jqzoom/jquery.jqzoom.css to a very large number, like 99999, but it won't help. I don't know what else to do so any help is really appreciated. Thanks.