I was looking at the PyGTK docs available at http://developer.gnome.org/pygtk/stable/ and found the default CSS to be far too "sparse," so to speak.  There was an awful lot of whitespace both vertically and horizontally which made it difficult to "take in" the documentation as easily as if it were just bare HTML.

Specifically I found that the margins were far too large, that the double "<br><br>" inbetween the top function definitions created too much space, and the argument descriptions in each function likewise took up far too much vertical space.  I ended up cobbling together a Stylish style to use for developer.gnome.org which makes things look much better for me, but IMO the default style should be more dense as well.

FWIW, the Style I'm using now:

  @namespace url(http://www.w3.org/1999/xhtml);
  @-moz-document domain("developer.gnome.org") {
    .body
    {
      width: 100% !important;
    }
    .content
    {
      width: 95% !important;
    }
    dl dt, table tbody tr td p
    {
      margin-bottom: 0px !important;
      margin-top: 0px !important;
    }
    br
    {
      line-height: .2em;
      height: .2em;
    }
  }

And also FWIW, after having put that together I noticed that the docs available at pygtk.org for the same content were much closer to how I'd ideally like docs to be presented.  For instance, http://www.pygtk.org/pygtk2reference/class-gtkwindow.html versus http://developer.gnome.org/pygtk/stable/class-gtkwindow.html

(And of course this kind of thing boils down to personal preference, but I figured putting in a bug might not hurt.)