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Scrolling Effect Problem

Hey guys,

I am a photographer and want to build a site for my business. I have a site from another creator which is my template and i want to recreate it. Here is the link:
I try to do that scroll transition where the text has this outline effect and gets solid while scrolling. I tried the same with the absolute position and z- index but it only is working for the first headline, after that the z index is to high, so the headline 2 is always solid.
Does anyone has an idea how i can recreate this effect? Maybe with an easy method or an add on?

Here is the link to my site:

Here is my site Read-Only: LINK
(how to share your site Read-Only link)