Something between r30123 and r30154 caused the inspector to be unstyled on Windows.
Created attachment 19092 [details] screenshot
I can reproduce this with r30154.
Reduced this down a little further: Works in r30146, doesn't work in r30151.
My guess is that r30147 is causing this <http://trac.webkit.org/projects/webkit/changeset/30147>.
I'll bet we need to add a case for ".css" files to the workaround at <http://trac.webkit.org/projects/webkit/browser/trunk/WebCore/platform/network/cf/ResourceResponseCFNet.cpp?rev=29841#L104>.
<rdar://problem/5737946>
Fixed in r30171.