- Replaced the dark mode checkbox with an Auto/Dark/Light selector in Preferences → Colors and added the new mode labels/setting metadata to match the combo box UI.

- Updated palette handling to respect the effective dark mode (including auto) when saving colors, applying themes, and refreshing user list styling.
- Added auto dark-mode tracking that listens to system theme changes and reapplies palette/styles live when Auto is selected, so updates happen without restart (including channel list styling updates via setup_apply_real).
- Synced the stored auto dark-mode state when preferences are applied, keeping Auto mode consistent after manual changes.
- Exposed a helper for keeping the Auto state synchronized from the GTK layer to preferences handling.

src/fe-gtk/fe-gtk.c

@@ -302,6 +302,35 @@ fe_system_prefers_dark (void)
 	return prefer_dark;
 }
 
+static gboolean auto_dark_mode_enabled = FALSE;
+
+static void
+fe_auto_dark_mode_changed (GtkSettings *settings, GParamSpec *pspec, gpointer data)
+{
+	gboolean enabled;
+
+	(void) settings;
+	(void) pspec;
+	(void) data;
+
+	if (prefs.hex_gui_dark_mode != ZOITECHAT_DARK_MODE_AUTO)
+		return;
+
+	enabled = fe_system_prefers_dark ();
+	if (enabled == auto_dark_mode_enabled)
+		return;
+
+	auto_dark_mode_enabled = enabled;
+	palette_apply_dark_mode (enabled);
+	setup_apply_real (0, TRUE, FALSE, FALSE);
+}
+
+void
+fe_set_auto_dark_mode_state (gboolean enabled)
+{
+	auto_dark_mode_enabled = enabled;
+}
+
 gboolean
 fe_dark_mode_is_enabled_for (unsigned int mode)
 {
@@ -369,6 +398,8 @@ create_input_style (GtkStyle *style)
 void
 fe_init (void)
 {
+	GtkSettings *settings;
+
 	palette_load ();
 	palette_apply_dark_mode (fe_dark_mode_is_enabled ());
 	key_init ();
@@ -379,6 +410,16 @@ fe_init (void)
 #endif
 	channelwin_pix = pixmap_load_from_file (prefs.hex_text_background);
 	input_style = create_input_style (gtk_style_new ());
+
+	settings = gtk_settings_get_default ();
+	if (settings)
+	{
+		auto_dark_mode_enabled = fe_system_prefers_dark ();
+		g_signal_connect (settings, "notify::gtk-application-prefer-dark-theme",
+						  G_CALLBACK (fe_auto_dark_mode_changed), NULL);
+		g_signal_connect (settings, "notify::gtk-theme-name",
+						  G_CALLBACK (fe_auto_dark_mode_changed), NULL);
+	}
 }
 
 #ifdef HAVE_GTK_MAC