Add a font-size type prop

I'm trying to create a font-size type of property that I would like to add to the dimensions sector. Doing this:

styleManager.addProperty('Dimension',{
	name: 'Icon Size',
	property: 'icon-size',
	type: 'integer',
	units: ['px', 'em', 'rem', '%']
});

Getting the value and all, but it's just showing an input box. Not one with the select option between the units. What am I doing wrong?