Hi Matthias,
I am struggling with this too and it’s a bit more complicated than just “setting the z-index”…
I too have a fixed element on my site (the login keyhole) which “floats” over background text, etc.
This means that I have to be sure that any interactive elements (buttons and form fields) are layered above it in the z. That includes the buttons that load the ACFFEF modal. But then the modal needs to be above everything, including its own launcher button, right?
When setting z-index as you probably already know the element has to have a position other than static. No problem. Relative usually works.
However there are two other problematic twists to z-index which is that it ALSO follows the hierarchy of parent child child child child AND there are circumstances when unpositioned “static” elements will stack on top of positioned ones on which you set a z-index and wonder why it doesn’t work…
In other words just giving the modal a high z-index didn’t solve the problem. Here’s why…
check these posts:
https://philipwalton.com/articles/what-no-one-told-you-about-z-index/
https://www.freecodecamp.org/news/4-reasons-your-z-index-isnt-working-and-how-to-fix-it-coder-coder-6bc05f103e6c/
You can see my problem here: https://www.artisanmodern.com/participate.
I have two separate ACFEFs. Getting them on top of my keyhole was not a problem, but getting them to not interfere with one another is so far only partly resolved.