Question:

Can Persistent Layer Pro be applied to a DIV declared in an external stylesheet?

Answer:

Yes, but the DIV definition will need the following CSS styles:
#someDIV {position:absolute; left:100px; top:100px;}

The initial top/left positions are yours to fill in to any number of pixels, but they do need to be defined. And don't forget to add the 'px' suffix to the left/top value.