Long dropdown menu won't scroll

My dropdown menus go below the bottom of the browser window but they won't scroll when I mouse over the lower part of the dropdown menu. How do I enable dropdown menu scrolling?

Ok, I figured out how to get them to scroll using another answer found in your support system:

#primary-menu ul ul {
overflow-y: scroll;
max-height: 80vh; /* recommended was 90vh, 80 seemed better */
}