Gtk+ 3.0 Client Side Theme

How to override user’s theme or I want my app with green buttons.

#include 

static gboolean
delete_event (GtkWidget *widget, GdkEvent *event, gpointer data)
{
	gtk_main_quit();
}

int
main (int argc, char* argv[])
{
  gtk_init(&argc, &argv);

  GtkCssProvider *provider = gtk_css_provider_new ();

  gtk_css_provider_load_from_data (
    provider, 
    "GtkButton {font: Monospace 10; background-color: rgba(0%, 76%, 0%, 0.6);}", 
    -1, NULL);

  GdkDisplay *display = gdk_display_get_default ();
  GdkScreen *screen = gdk_display_get_default_screen (display);

  gtk_style_context_add_provider_for_screen (
    screen, GTK_STYLE_PROVIDER (provider),
    GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
  
  g_object_unref (provider);

  GtkWidget *window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_container_set_border_width (GTK_CONTAINER (window), 10);
  g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (delete_event), NULL);

  GtkWidget *button = gtk_button_new_with_label("GtkCssProvider load from data");
  gtk_container_add (GTK_CONTAINER (window), GTK_WIDGET (button));
  gtk_widget_show_all (GTK_WIDGET (window));

  gtk_main ();	
  return 0;
}