Sticky Element doesn't work in Laytheme

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I want to have an image sticky on top of my page when I scroll it down, I tried
"position: -webkit-sticky;
position: sticky;"
and it worked on codepen but not in my laytheme page.
How can I do it?

Dear @gabriel_lam
the sticky does not seem to work. Maybe in the forum you can find some solutions. You are not the first.
Best!
Marius