Z-index Module in modal

Hello,
on www.vollebregtbrommobiel.nl/aixam-store-nederland I'm using the button "OKTOBER ACTIE!" to trigger the Module in Modal.
But as you can see the images of the small slideshow are on top of the Module in Modal. I've tried to change the z-index of this by adding to the custom css:
#jbounce-jmodal {
z-index:99999999;}
But unfortunately without luck.
How can I fix this?
Thanks!
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