How do you set a class factory in CSS styles?

I've been having trouble setting the item renderer of a Spark DataGrid in CSS and then I remembered the compiler creates a class factory for it.

This CSS does not work:

.myGrid {
    itemRenderer: ClassReference("myItemRenderer");
}

but declaring it inline it does:

<s:DataGrid itemRenderer="myItemRenderer" />

I found this setStyle code and put it in the constructor but it doesn't work:

    public function DataGrid() {
        super();

        setStyle("itemRenderer", new ClassFactory(myItemRenderer));
    }

I've created a new control and I want to use my custom renderer as default. So all the styles are set in the defaults.css.

I can't set a class factory in CSS for this property. I think the property needs to be a IFactory and defined as a style.

I can set an item renderer with the DataGrid. I can set it in the constructor using:

public function DataGrid() {
    super();

    itemRenderer = new ClassFactory(myItemRenderer);
}

or in the DataGrid skin:

<s:Scroller id="scroller" minViewportInset="1" hasFocusableChildren="false" height="100%">
    <!--- @private -->
    <s:Grid id="grid" itemRenderer="MyGridItemRenderer">

    </s:Grid>                    
</s:Scroller>