Defining custom user link icons

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This is one of those questions I feel I should be able to answer myself, but I've searched in various places and come up empty.

In a stylesheet, is it possible to define some custom icons for user links and have others be the system default? At present I'm using custom icons for Dreamwidth users and communities, but external service users' links have no icons; there's just a blank space where the stylesheet specifies the image height and width, etc. So either there's something I need to change in my existing CSS or I need to add the location of all the other icons. But I don't know what they are since s.dreamwidth.org/img/ doesn't allow directory listing (which makes sense), and I can't find a list of all the image file names.

I should add that I'm using a stylesheet made by sarken that I've modified mostly through trial and (much) error because no matter how hard I try my brain just refuses to grasp this stuff.

( CSS under the cut )

Please help my scrambled brain?