Gtk::Frame transparent background

[Carlo Ascani <carlo ratm gmail com>]

How is it possible to rendere transparent background for Gtk::Frame?
Something like this:
The Frame "Levels" for instance
http://linux-sound.org/images/blog/full-size/2-shiny-calf.png

-- 
Carlo Ascani
La politica pratica consiste nell'ignorare i fatti. (Henry Adams)
C programmers never die. They are just cast into void.
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