One thing, don't use the margin shorthand. Use the separate margin lines such as margin-top: margin-right:. It's a lot easier to read the CSS that way.
As for div.poetry p, 3em is too large. Think of reading this on a small cell phone screen. You already have a 2em margin. 1em is better. Also, you don't need padding and you don't need left align.
Code:
blockquote.poetry {
margin-top: 1em;
margin-right: 0;
margin-bottom: 1em;
margin-left: 2em;
}
blockquote.poetry p {
margin-top: 0;
margin-right: 0;
margin-bottom: 0;
margin-left: 1.5em;
text-indent: -1.5em;
}
blockquote.poetry p.indented {
margin-left: 2em;
}
blockquote.poetry p.first {
margin-top: 1em;
}