Make overlay scrollbars?

Is it possible to make an overlay scrollbar?

Basically, I have a parent div with child divs inside. I'd like to make the vertical scrollbar overlay on top of the child divs instead of the scrollbar occupying space in the parent div and pushing the child divs to the left.

I'm planning to make the scrollbar transparent and only show it when the parent div gets hovered.

Is that possible with just css or does it need javascript? Please help thanks