Buttons Not Clickable in Flutter Parallax Scroll

I am trying to build Parallax Effect in my app, Most of the people suggest using Stack + Positioned + Any Scrollable widget in my case ListView.
So the issue is that due to Stack widget my buttons are not clickable as the transparent ListView widget is always on top of them.
Here's my pen:
https://codepen.io/sukhcha_in/pen/JjKYJpd
Please suggest some better way of doing it :(

Solution 1: Sukhchain Singh

Solved! Not sure if this is the best solution but kinda works :P
Here's the pen: https://codepen.io/sukhcha_in/full/JjKYJpd

double myChildSize = 500.0;
double appbarHeight = appBar.preferredSize.height;