I'm trying to make some new themes. Unfortunately I can't find any information via google. Perhaps I suck an coming up with search terms.

What I'm looking for is an explanation of the *.css files. There seems to be features in them that goes beyond what I've learned messing around with web pages.

I don't understand the things like:
color: shade (@bg_color, 0.6);
text-shadow: 0 1 alpha (shade (@bg_color, 1.25), 0.5)
what are these -unico values?

And in lines like:
GtkComboBox.combobox-entry .button,
are all buttons, active buttons and insensitive buttons affected by what is within the curly braces or is it just the ones within a combobox.

What I also would like is a picture of the components (I believe the term might be "widgets") labeled with what they are called in the files.

Are these files documented anywhere?