Parallax-Scrolling | Code to accompany the tutorial in Smashing Magazine | Learning library

While I am trying to do Collapsing Toolbar Layout I got the error on contentScrim not found. This is my XML file.

I'm trying to use both Toolbar and TabLayout with CollapsingToolbarLayout but I'm getting a very strange behavior with the tab layout. The idea is to have the TabLayout with a transparent background when the Toolbar is expanded, and when collapsed, to be under the Toolbar like any other Activity with both Toolbar and TabLayout.

I would like to implement a CollapsingToolbarLayout like this:

The challenge here is that I need to have a custom Toolbar with a gif as background and therefore I need an ImageView as background for the Toolbar. You can see my implementation in the following xml:

I want to make a slider like a demo: https://ihatetomatoes.net/demos/simple-parallax-scrolling-tutorial/

I can do the parallax option but I need the effect of the content of the demo. When scroll I need to fade out the content in Slider Revolution.

Regards,

I'm learning how to create a scroll parallax effect following this guide. So far so good, but then I realize that my background position is set to '50%'(center). So when I run my js, the background position unit is changed from % to px hence it position is not what I expected.

How can I write the code so the background position change in percentage?

Here is the code: