Utterscroll works in nested scrollbars. Click and drag :-) But not too close to this text, becauase then you'd select the text insted.

Also test to use the scrollbars. However, There might be problems with the scrollbars however, unless you style the containing element with position: relative or position: absolute.
(In this example, the wrapping blue box has position: relative.)

Do you think this <div> has any right edge? Do you think it has any bottom?

This is the right bottom, it did exist and you have found it :-)