Why is the scrollbar disappearing in the modal window?

Question

JavaScript

In general, the situation is as follows:

https://beta.smpl.vc/investicii/ - if you click on "Details", a modal window is displayed, it is rotated with the keyboard keys "up" "down" and the mouse wheel, but there is no scrollbar itself ( this is in the google browser), and a scroll bar is displayed in the muzzle, but if you click on this bar, the window closes.

Because of what could it be? After all, the window itself is scrollable (they simply do not fit in the height of the monitor).

Answer 1

Because position is "fixed"