This is what I have, I have left div, and a right div. The left div is a fixed width, and floated left. The right Div is a "display: block" to make it full width, and has a margin on the left to compensate for the left div. Both of the boxes have a fixed height, and need to be scrollable (the contents inside). I add an overflow-y to the Left div successfully. However when I add overflow-y: auto to the right div, the div no longer spans the whole div.
Before adding Overflow: http://jsbin.com/asecuy/
After adding Overflow: http://jsbin.com/asecuy/2