This will set the positioning and create a down pointing arrow. The numbers are custom and can be adjusted to change the size of the arrow and its position.
.overviews-list > li.active > ul.submenu > li.active {
position: relative;
}
.overviews-list > li.active > ul.submenu > li.active:after {
position: absolute;
content: "";
width: 0px;
height: 0px;
border-top: 15px solid white;
border-right: 15px solid transparent;
border-bottom: 15px solid transparent;
border-left: 15px solid transparent;
top: 25%;
right: 10px;
}