[Theme 2014 modified] photo gallery hides navigation

Can you post a link to your site?

the site is on a temporary domain during the work:

https://aspara.fr/les-galeries/nouvelles-pieces/

I have not been able to find any clues to this problem yet.

Try using this code:

#primary-navigation ul li ul {
    z-index: 80;
}

Perfect! Thank you!