Floating Div Size for My DESIGNS

Is there a way to specify the size of the popup for My DESIGNS without affecting the size of the clipart library popup?

You can style its size with it's external class. Like this in your DirectCss:

.tabs_floatingdiv_extclass_owndesigns {
    width: 70% !important;
    height: 70% !important;
    left: 15% !important;
    top: 15% !important;
}