Hey there,

judging from the code this doesn't seem to be a true parallax (I written pure css+html one). Parallax requires two moving elements with different speeds relative to each other. Your example seems to be basically a fixed position image (scrolled position in this case) with a scrollable element on top.

If you are interested in these things, pure css&html parallaxes is, as far as I know, always based on perspective. Check out an example here (it's a quite nice to learn from): https://codepen.io/keithclark/pen/JycFw

For the future, I'd advice you to put your demo e.g. here: https://codepen.io/ so we can all see them working first hand.