Box with text inside (in-scroll) - relative height to bottom

Hi there,

I have a box with text content (lorem ipsum in the pic) which fits to the height of the group its sitting in.

I want the box’s height (with the text inside) to always fill the whole height of the window until it reaches the floating group at the bottom (red).

So while the window gets shorter and the floating group (red) moves its way up, the height of the box should be reduced.

I thought about gibing the box 0 max height and margin to the bottom but that expands the whole window and 100% of text shows up (so scrolling within the box is disabled)

Any thoughts?