That's just background-image. You can set their position too, as you might expect. We'll shorthand it:
url(image-one.jpg) no-repeat top right,
url(image-two.jpg) no-repeat bottom left;
I snuck background-repeat in there just for fun. Another one you might not think of setting for multiple different backgrounds, though, is background-clip. In this linked article, Stefan Judis notes that this unlocks some pretty legit CSS-Trickery!