[retro-gtk] demo: Use dark theme

[Adrien Plazas <aplazas src gnome org>]

commit 0343fe69cb2634b4354b78c81b8d0df1ecbe1471
Author: Alexander Mikhaylenko <exalm7659 gmail com>
Date:   Tue Jan 15 23:14:42 2019 +0500

    demo: Use dark theme

 demos/retro-demo.c | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/demos/retro-demo.c b/demos/retro-demo.c
index e67bed0..a0b2232 100644
--- a/demos/retro-demo.c
+++ b/demos/retro-demo.c
@@ -85,11 +85,15 @@ retro_demo_activate (GApplication *application)
   RetroDemoApplication *self;
   GtkWidget *window;
   RetroCoreView *view;
+  GtkSettings *settings;
 
   self = RETRO_DEMO_APPLICATION (application);
 
   g_signal_connect (self->core, "log", (GCallback) retro_g_log, NULL);
 
+  settings = gtk_settings_get_default ();
+  g_object_set (G_OBJECT (settings), "gtk-application-prefer-dark-theme", TRUE, NULL);
+
   view = retro_core_view_new ();
   retro_core_view_set_core (view, self->core);
   retro_core_view_set_as_default_controller (view, self->core);