From the
Mobipocket page:
The indentation of the first line of a paragraph can be forced by adding the width of a paragraph :
<p width="X"> (pixels), <p width="X%">,<p width="Xem"> or <p width="Xpt">
or
text-indent: X (%, em, pt, or nothing for pixels) with a style sheet.
X is an INTEGER and can be positive or negative for positive or negative indentation.
(and it's mostly the same for other lengths)