Plug-on scrolling behavior for a container.
Use this to style containers, such as pop-up menus, to be scrolling, and
automatically keep the highlighted element visible.
To use this, first style your container with the desired overflow
properties and height to achieve vertical scrolling. Also, the scrolling
div should have no vertical padding, for two reasons: it is difficult to
compensate for, and is generally not what you want due to the strange way
CSS handles padding on the scrolling dimension.
The container must already be rendered before this may be constructed.