why i can't set background of widget?

[gxw <szg309 sina com>]

After run the following simple code,the button background is black,and can't see "Hello World",who can tell 
me the reason?

Thank you!

#include <gtk/gtk.h>

int main( int argc,char *argv[] )
{
    
    GtkWidget *window;
    GtkWidget *button;
    GtkStyle *style;
    
    gtk_init (&argc, &argv);    
    
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);      
        
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);    
    
    button = gtk_button_new_with_label ("Hello World");
    style=gtk_style_new();
    style->bg[GTK_STATE_NORMAL].red=0;
    style->bg[GTK_STATE_NORMAL].green=0;
    style->bg[GTK_STATE_NORMAL].blue=255;
    gtk_widget_set_style(button,style); 
    gtk_container_add (GTK_CONTAINER (window), button);    

    gtk_widget_show (button);  
    gtk_widget_show (window);    
    gtk_main ();    
    return 0;
}