use the new dark mode settings

data/resources/ui/preferences.ui

@@ -15,7 +15,7 @@
         <property name="icon-name">applications-system-symbolic</property>
         <property name="title" translatable="yes">General</property>
         <child>
-          <object class="AdwPreferencesGroup">
+          <object class="AdwPreferencesGroup" id="dark_theme_group">
             <property name="title" translatable="yes">Appearance</property>
             <child>
               <object class="AdwActionRow">

src/application.rs

@@ -3,9 +3,10 @@ use crate::{
     models::{Keyring, ProvidersModel, FAVICONS_PATH},
     widgets::{PreferencesWindow, ProvidersDialog, Window},
 };
+use adw::prelude::*;
 use gettextrs::gettext;
 use glib::clone;
-use gtk::{gio, glib, prelude::*, subclass::prelude::*};
+use gtk::{gio, glib, subclass::prelude::*};
 use gtk_macros::{action, get_action};
 
 mod imp {
@@ -196,10 +197,12 @@ mod imp {
                             }
                         },
                         "auto-lock-timeout" => app.restart_lock_timeout(),
+                        "dark-mode" => app.update_color_scheme(),
                         _ => ()
                     }
                 }),
             );
+            app.update_color_scheme();
         }
 
         fn activate(&self, app: &Self::Type) {
@@ -316,4 +319,16 @@ impl Application {
             id.remove();
         }
     }
+
+    fn update_color_scheme(&self) {
+        let manager = self.style_manager();
+        if !manager.system_supports_color_schemes() {
+            let color_scheme = if self.imp().settings.boolean("dark-mode") {
+                adw::ColorScheme::PreferDark
+            } else {
+                adw::ColorScheme::PreferLight
+            };
+            manager.set_color_scheme(color_scheme);
+        }
+    }
 }

src/widgets/preferences/window.rs

@@ -44,6 +44,8 @@ mod imp {
         pub auto_lock: TemplateChild<gtk::Switch>,
         #[template_child(id = "dark_theme_switch")]
         pub dark_theme: TemplateChild<gtk::Switch>,
+        #[template_child]
+        pub dark_theme_group: TemplateChild<adw::PreferencesGroup>,
         #[template_child(id = "lock_timeout_spin_btn")]
         pub lock_timeout: TemplateChild<gtk::SpinButton>,
     }
@@ -71,6 +73,7 @@ mod imp {
                 lock_timeout: TemplateChild::default(),
                 backup_group: TemplateChild::default(),
                 restore_group: TemplateChild::default(),
+                dark_theme_group: TemplateChild::default(),
                 file_chooser: RefCell::new(None),
             }
         }
@@ -161,6 +164,10 @@ impl PreferencesWindow {
     fn setup_widgets(&self) {
         let imp = self.imp();
 
+        let style_manager = adw::StyleManager::default();
+        imp.dark_theme_group
+            .set_visible(!style_manager.system_supports_color_schemes());
+
         imp.settings
             .bind("dark-theme", &*imp.dark_theme, "active")
             .build();

src/widgets/window.rs

@@ -250,15 +250,6 @@ impl Window {
                 title_stack.set_visible_child_name("title");
             }
         }));
-
-        let gtk_settings = gtk::Settings::default().unwrap();
-        imp.settings
-            .bind(
-                "dark-theme",
-                &gtk_settings,
-                "gtk-application-prefer-dark-theme",
-            )
-            .build();
     }
 
     fn setup_actions(&self, app: &Application) {