This is because your CSS declaration is wrong. You should separate the selectors with comma ,
:
.pop-div, .popover-content {
not
.pop-div .popover-content {
in this case .pop-div
is unnessecary, you only need
.popover-content {
height: 50px;
overflow-y: scroll;
}
see fiddle -> http://jsfiddle.net/tv5Vu/