Panel – scrollbar and scrolling by page

I have a panel – let’s say 3 columns of data, 2 visible, horizontally scrolled.

Associated scrollbar behaves as only the selected column were visible – scroll handle is 1/3 of width. Is there a way to make it behave properly – so that the scroll handle is 2/3 of width?

Another thing – is scrolling panel by page (scroll only when going off-screen with selection) already implemented/good solution found? The latest posts about it are years old.