W3Schools has an example of formatting XML with CSS at http://www.w3schools.com/xml/xml_display.asp
It's pretty much as you'd expect, except that no display properties are implicit, as they are with HTML. eg with this:
<something>Here is some text</something>
You can go:
and so on.
What you want is XSL - http://www.w3schools.com/xsl/default.asp