It is using CSS for cursor and PNG for the arrows.
Code like
cursor: url("../img/cursor-right.png") 10 10, e-resize;
All we would do is add two transparent boxes down the middle and each would have a Name so the CSS could latch on.

With JavaScript, one could detect where the pointer was and change from that.
The overlays, with Filename="..." would be simpler.

Acorn