Are you 100% sure? Of course there are lots of ways to save information about themes. I’m almost sure that without C/C++/C# or similar you will not be able to extract icons from *.dll files, but it’s not like that all things are written in *.so or binary files …
Take a look at this fragment:
[Colors:Button]
BackgroundAlternate=77,77,77
BackgroundNormal=49,54,59
DecorationFocus=61,174,233
DecorationHover=61,174,233
ForegroundActive=61,174,233
ForegroundInactive=189,195,199
ForegroundLink=41,128,185
ForegroundNegative=218,68,83
ForegroundNeutral=246,116,0
ForegroundNormal=239,240,241
ForegroundPositive=39,174,96
ForegroundVisited=127,140,141
I found it in: ~/.kde4/share/apps/color-schemes/Breeze\ Dark.colors. Also in KDE/Plasma and GTK+ icons are not even in zip files, for example:
/usr/share/icons/breeze-dark/actions/32/window-close.svg
Looks like that GTK+ have theme information in CSS files … well … there could be simpler option, but it’s not also that hard to parse it … At least there is no NIF needed:
/usr/share/themes/Breeze-Dark/gtk-3.20/gtk.css
I’m not sure how it looks like in MacOS and in Windows (in details) - it’s why I want someone to take literally full research - i.e. collect all information about vm and app theme files - their format, how to parse them, if NIF is required etc.
If we are talking about button in this case it’s component:
Yeah, it could be hard to do it from 3rd-party library, so I would like to see @boydm opinion on this. At end we can write a fork. I would strongly don’t like to, but it’s not like that all of what I have in mind is extremely hard to implement (just look about theme files - unlike what you said it’s pretty easy to use them without even need any NIF).
Sorry, but I don’t want to wait for Windows 20 for such simple thing like Alt + mouse buttons to move/resize window quickly. If it’s possible to do awesome things which could work in any OS then it’s definitely reasonable - at least for me. I believe that @OvermindDL1 would agree as well.
Well … maybe in some specific cases, but not on those I was looking for (KDE/Plasma and GTK+ as already described). Sometimes we have even SVG files with could be useful as well.
Also it’s not like that you need to understand all frameworks in the world. Sometimes you would need to write some NIFs, but it’s not like that whole world is build with binary blobs. 
Of course it’s not “5 min” easy work (it’s why I created this topic), but it would definitely give us a lot of flexibility which is always good if it’s not overcomplicated.
