Image drag n drop

I’m trying to learn how to setup a drag and drop activity. I have setup a codepen here of what I have so far https://codepen.io/monkeycrane2010/pen/PoGKpLZ . If you drag any of the images into the box below the screen, it detects the drag event. But I can’t figure how how to add the image to the box when it is dropped. Anyone have any ideas?