Thank you very much, that did work. I do have a couple of other questions though.
First, a friend of mine provided some other code which basically does the same thing.
article.post.hentry { border-bottom: 1px solid #fff; padding-bottom: 30px; margin-bottom: 30px; }
article.post.hentry:last-child { border-bottom: none; padding-bottom: 0; }
I don’t understand CSS well enough to know why these two bits of code do basically the same thing. Why does .archive .type-post modify exactly the same thing as article.post.hentry?
Second, is there a way I could use an image as the divider, rather than a 1px line? I have a horizontal line image that I use as a divider on pages and in posts. Is it possible to use that instead?
Thanks again for your help!