Demo/Application: rely on Granite.StyleManager (#287)

Author: danirabbit

demo/Application.vala

@@ -28,18 +28,12 @@ public class Application : Gtk.Application {
         );
     }
 
-    protected override void activate () {
-        var granite_settings = Granite.Settings.get_default ();
-        var gtk_settings = Gtk.Settings.get_default ();
-
-        gtk_settings.gtk_application_prefer_dark_theme =
-            granite_settings.prefers_color_scheme == Granite.Settings.ColorScheme.DARK;
-
-        granite_settings.notify["prefers-color-scheme"].connect (() => {
-            gtk_settings.gtk_application_prefer_dark_theme =
-                granite_settings.prefers_color_scheme == Granite.Settings.ColorScheme.DARK;
-        });
+    protected override void startup () {
+        base.startup ();
+        Granite.init ();
+    }
 
+    protected override void activate () {
         var window = new MainWindow (this);
         window.present ();
     }