GTKD - overrideBackgroundColor of Button doesn't work

[TheDGuy via Digitalmars-d-learn]

On Wednesday, 15 June 2016 at 20:49:02 UTC, Gerald wrote:
> On Wednesday, 15 June 2016 at 09:03:45 UTC, TheDGuy wrote:
>> Hello,
>> why does this code not work?
>>
>>         RGBA rgb = new RGBA(1,0.5,0.5,1.0);
>>         Button btn_1 = new Button("Start");
>>         btn_1.overrideBackgroundColor(StateFlags.NORMAL, rgb);
>>
>> The color of btn_1 just doesn't change.
>
> https://developer.gnome.org/gtk3/stable/GtkWidget.html#gtk-widget-override-background-color

Thanks for your reply, i now tried to use CSS instead:

import std.stdio;
import std.file;
import gtk.Main;
import gtk.MainWindow;
import gtk.CssProvider;
import gtk.Button;
import gdk.Display;
import gdk.Screen;
import gtk.StyleContext;

class Window : MainWindow{
     this(int width, int height, string title){
         super(title);
         setDefaultSize(width, height);
         Button btn = new Button("Test");
         btn.setName("CssName");

         string cssPath = "test.css";

         CssProvider provider = new CssProvider();
         provider.loadFromPath(cssPath);

         Display display = Display.getDefault();
         Screen screen = display.getDefaultScreen();
         StyleContext.addProviderForScreen(screen, provider, 
GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);

         add(btn);
         showAll();
     }
}

void main(string[] args){
     writeln(getcwd());
     Main.init(args);
     auto win = new Window(250,250,"Tutorial");
     Main.run();
}

This is my CSS:
GtkWindow{
	background-color:blue;
}
#CssName{
	-GtkWidget-focus-line-width:0;
	background-color:green;
	color:green;
}

The text color is green but the button background color is still 
default-gray!
I am also wondering how it is possible to change the button color 
at runtime? In my opinion i don't think that CSS-based style has 
alot of advantages over the commonly used object functions.