How to Fixed UI and Animation On Scroll Down

I’m really trying to make this work but I can’t seem to find an answer.
I’m trying to animate a Lottie while scrolling down but the whole page must be wrapped like in this picture:

In my Read-Only you can find two pages. The first one works great, but it doesnt have the fixed wrapper like what I need. The second page is my failed attempt to make it work.

Read Only:

Is there a way to have this UI wrapper (100vh) and still making the lottie on scroll animation work? Is there a work around? I tried one in the third page but can’t make it work (Like a fixed something above it all?)

Thanks in advance!