I wanted to share this one hour work with others in a hope to receive advice and maybe help others at the same time
It's simple gtkrc file, which should replace "/usr/share/themes/Adwaita/gtk-2.0/gtkrc" - nothing more required

Two sceenshots are provided:
1. Nautilus (gtk3) and Synaptic (gtk2) with my equinox tweak
2. Nautilus (gtk3) and Synaptic (gtk2) with default (Adwaita) clearlooks gtk2 theme


Here is kind of story:
I use Ubuntu and dislike default "orange" theme. In previous 11.04 (gtk2) distro I was using excellent oxygen-gtk theme engine and was very happy with it - oxygen style but in gtk world. Now as time goes by, I use Ubuntu 12.04 (gtk3) and unfortunately oxygen-gtk can't cope with it at this moment. I reported some bugs to it, but there are lots of issues, and it doesn't look sane to me to report every issue just now

So what to do?
I use default gnome-shell theme Adwaita, which is IMHO very nice, but it's gtk2 version (clearlooks) just sucks too much in comparison (see second screenshot). I know it's not just me because I even witnessed some efforts (Google it) to mimic this theme in gtk2 world, maybe not worth mentioning because it looks like patchwork

Here is my post:
I took very well known equinox light theme, and play around it until I could. Result is not bad IMHO, but I would like advice on (main problem):

1. how to make buttons w/o shadow (mimic Adwaita style)

There are other issues of course, like toolbar gradient:

2. how to define toolbar gradient

w/o using images or similar awful approaches. BTW it can be turned off by setting "toolbarstyle = 4" in provided gtkrc.

Last major thing left, is list headers (in gtkrc defined as "listviewheaderstyle"). There is no info anywhere how to tweak those:

3. How to define list headers background