eliot wrote: Hi Vero,
As I said, we can't do anything without a link to your site or at least a bigger screenshot.
From what I can see, I think it comes from your template and the menu which is using specific css rules.
In this case we can't do anything since it will be over every popup so the only solution is to edit your template css.
I think that´s something about z-index. In template horizonyal menu z-index=100000. But i didn't find popup z-index. If I do this on = 100100, than popup wil be up. That's right or no? But I am looking for popup in custom front-end CSS and don't know where is it...