I use the free css plugin from zeroqode, easy and reliable. I haven’t touched the classify one.
The parallax is available on the page with the background set to image. Out I believe in a group with the same settings but I don’t recall on the top of my head and am not near my computer.
tried the css plugin and had the same issues.
The parallax effect is for the page only and not for applying effects to individual element unfortunately … So I will keep trying to find a solution.