application: Support dark style preference

Depend on libhandy 1.5.0.

src/core/gcal-night-light-monitor.c

@@ -67,10 +67,12 @@ on_night_light_proxy_properties_changed_cb (GcalNightLightMonitor *self,
       activev = g_dbus_proxy_get_cached_property (proxy, "NightLightActive");
       active = g_variant_get_boolean (activev);
 
-      g_object_set (gtk_settings_get_default (),
-                    "gtk-application-prefer-dark-theme",
-                    active,
-                    NULL);
+      if (active)
+        hdy_style_manager_set_color_scheme (hdy_style_manager_get_default (),
+                                            HDY_COLOR_SCHEME_PREFER_DARK);
+      else
+        hdy_style_manager_set_color_scheme (hdy_style_manager_get_default (),
+                                            HDY_COLOR_SCHEME_PREFER_LIGHT);
     }
 }
 

src/gui/gcal-application.c

@@ -362,6 +362,9 @@ gcal_application_startup (GApplication *app)
   /*  initialize libhandy */
   hdy_init();
 
+  hdy_style_manager_set_color_scheme (hdy_style_manager_get_default (),
+                                      HDY_COLOR_SCHEME_PREFER_LIGHT);
+
   /* Startup the manager */
   gcal_context_startup (self->context);