I'm not sure writing a CSS stylesheet for TEI document is a good idea:
you should consider first transforming the XML TEI document, which is
a complete format, into a rendition format (like XHTML) using XSLT,
and then (optionnaly) use CSS.
Actually, I'm looking for a CSS stylesheet for use with XXE. There is
none included with the software, as is the case for DocBook.
Also, in my experience, CSS stylesheets are a very convenient,
although limited way of previewing an XML document while authoring the
document. It's sufficient when there is no real transformation
involved (ie, data manipulation, such as sorting).