Drag a shape to move it, and click the sheet to select nothing. Arrow keys nudge whatever is selected; Delete takes it off. Setting the sheet crops rather than scales: nothing is resized, the sheet grows and shrinks about its middle, and only a shape left outside a smaller one is pulled back to its edge.
An overlap here is a region and not a blend mode. The tool works out which shapes cover which patch of the sheet, mixes those colours once, and prints the patch as a flat opaque shape clipped to it — so the exported file is the picture on the screen, arrived at the same way, and it opens the same in a browser, in Illustrator or in anything else that reads plain SVG.
Nothing here has a z-order, because ink does not have one. A patch covered by cyan and by yellow is green whichever plate went down first, and the same is true of two beams in a dark room. The order shapes were added in decides which one a click picks up and nothing else about the sheet.