ComboBox Menu background colour

[Steve Holmes <mrsteve holmes gmail com>]

Does anyone know how I can set the background colour of the menu in a ComboBox using CSS? I have  everything working to use the css file but I can't figure out how to reference the popup menu in the ComboBox. I was thinking it would be something like this:

GtkComboBox.popup-menu {
    color: red;
    background: black;
}

This does not work. I can set the style of the selected entry with:

GtkCombBox {
    color: blue;
    background: yellow;
}

Is there some documentation somewhere that would list all the objects we can reference using the css provider? The examples just show the basics.