Here are 2 examples of the div tag that I got from Mobipocket. The style attribute works even though it's not listed as supported attribute.
<div style="border: 1px solid black; background-color: gray;"> </div>
<div align="center" bgcolor="#FFEBD6"> </div>
Here is a link to info on the div tag (not all will work in Mobipocket):
http://www.w3schools.com/tags/tag_DIV.asp
I think it might be best to put each line of poetry in its own set of tags. If you need more indentation, I would recommend using (the non breaking space character). This will adjust better when changing the font size.