[Vala][Styling] Dark variant question

[Filip Lamparski <matka poohatka gmail com>]

Hello,

I'm writing an application which allows users to apply various filters 
to images and share them to social networks. I would like it to use the 
dark theme variant, like Totem or EOG. I tried looking at EOG code to 
figure it out, but no dice.

I figured something out, and it's half-working, which creates a 
rather... interesting effect (see attachment).

Code:

var darkprovider = 
CssProvider.get_named(this.get_settings().gtk_theme_name, "dark");
var winstyle = this.get_style_context();
winstyle.add_provider(darkprovider,STYLE_PROVIDER_PRIORITY_APPLICATION);

My question is, how do I fix this, so that all widgets use the dark 
variant, including window decoration?