Why doesn't div stretch when align-self: stretch?

Question

HTML

Why doesn't the bottom div stretch when align-self: stretch ?
I would like the height of the top div to automatically change depending on the content,
and the height of the bottom div to automatically stretch to the end of the parent (in this case, to the end of the page).
https://jsfiddle.net/2xdvq7dL/

Answer 1

https://jsfiddle.net/2xdvq7dL/1/