If you need to position a
background-image in CSS 20px from the left and 10px from the top, that's easy. You can do
background-position: 20px 10px;. But what if you wanted to position it 20px from the right and 10px from the bottom?
Let's also assume we don't know the exact width and height of the element, which is likely, because fluid layouts and dynamic content. If we did, we could just do a little scratchpad math and …