Clone the node and visually hide it rather than cloning an incomplete set of styles

Scenario: You have a parent container with two DOM nodes in it, one `float: left` and one `float: right`. You want to `position: sticky` one of the floated nodes. 

This scenario is supported natively but the polyfill's current behavior inserts a static node of the correct dimensions but neglects it's float. This just shallow clones the node to inherit all of the original positioning. (Though, I suppose we could also just copy over the float as well, instead)

In addition I've removed the z-index declaration which seems arbitrary and should probably be handled in CSS to begin with. (Imagine one has a fixed header with a lower z-index than 999 and you see the problem with that)