Hello Marcel,
thank you for your answer and sorry for not responding earlier, I was rebuilding my site.
I still have the same problem with the header coming in front of the image. It’s less annoying because I set the header to be transparent but I can’t close the image with the cross on the upper right corner. I tried the code in your first answer but it doesn’t work.
here is the adress of one page : https://alpha-draconis.fr/?p=290 but you can also check the full site if you need to : https://alpha-draconis.fr
Thanks again for your help
Best regards,
Alexandre