How to make the effect of smooth extension of the block (inside the example)?

Question

JavaScript

Good afternoon!

How to make a pull out block effect like on johnpatrickgiven.com ?
How to understand which plugin was used? (what happens when you click on the button as in the picture)
Take this site as a basis and redo it for yourself.

Answer 1

There seems to be nothing moving anywhere, just a scrolling animation. And the background does not move due to background-attachment: fixed .