Pop UP Custom Value Height

[sjfp]

How can i adjust the size (Height) of a popup box. I have 7 custom values, but the pop up only show 5 of them, so you have to use the slider to show the missing 2 values.
I there a way to show all 7 custom values so the user does need to use the slider ?
Also need to enlarge the popup and center all popups to the center of the screen

Sorted, used the following in CSS

.control-vselect .popover-content .nav {
  max-height: 250px;
  overflow-y: auto;
}