Some comments:
Code:
@page {margin: 1.3em}
I think that's too large a margin, and you probably don't want it to change with font size. For ebook readers, a minimal margin is usually a better idea, something like 2mm.
Code:
body { font-family: "Garamond"; }
Avoid specifying a font-family unless for some particular technical or stylistic effects. The main text font is probably something the user would like to set him/herself, and not have it forced by the book. Besides, most ebook readers won't have a "Garamond" font available anyway.
Code:
p { text-align: left; }
Personally, I prefer justified text, but I know some people prefer left-aligned, especially in small screens. In any case, that's also something better left to the user, do not set any alignment to normal paragraphs.
Code:
intro { letter-spacing: 0.09em; }
The letter-spacing property is not in the ePub 2.1 spec. It's not a big deal, readers that don't support it (because they are not required too) will just ignore it.
Code:
<p class="tom"> </p>
Do not do that. You just want some vertical space, use vertical (top/bottom) margins, or a block element with fixed height. That's not a paragraph and there's no content to have there, don't add vertical space with "empty lines".