In Internet Explorer, the default stylesheet used to display XML documents can be found at:
res://msxml.dll/DEFAULTSS.xsl
In Firefox, the equivalent can be found at
chrome://global/content/xml/XMLPrettyPrint.xsl
Is there something equivalent in Chrome?
The CSS for the XML viewer specifically is https://code.google.com/codesearch#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/xml/XMLViewer.css. That file, in combination with https://code.google.com/codesearch#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/css/view-source.css, should give you all the detail you need.
Also remember that you're able to use the Web Inspector on XML files to see the rendered HTML, which should help you piece together exactly how the view works.
Do have a look at:
https://code.google.com/codesearch#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/xml/XMLViewer.js
Also, if you want to see yet another XSLT transformation that produces precise and good-loking in the browser XML representation, do have a look at the transformation used by the XPath Visualizer -- both for IE and for FF.
