How to draw this window?

Can I create a window without this topbar? :

I want a window like this:

Here they say you could try:

gtk.Window.set_decorated(False)

You could also do

window.set_type_hint(gtk.gdk.WINDOW_TYPE_HINT_SPLASHSCREEN)

but that doesn't have rounded corners either, at least on my theme. As eumiro says, that depends on the theme settings.