My scrollbar slider (or foreground) doesn't have the full range of motion of the background. It only moves a tiny bit, relative to the motion of the scroll view it's attached to. It interpolates over that range, but I'd like to move along the full background bar.
See here:

The image on the left is the scroll bar scrolled all the way to the top, and the one on the right is it scrolled all the way down. What I want is for when it is scrolled all the way down is for the slider to be at the bottom of the bar.
How can I get its range of motion to match the background's height?
Thank you.