Fix gtk theme to work with dark mode

config/headful.nix

@@ -36,10 +36,18 @@
   # Suppress greetd's default virtual terminal log spam.
   systemd.services.greetd.serviceConfig.LogStandardStream = "journal";
 
-  # XDG Desktop Portals (used for wayland screen sharing, file pickets, etc.)
+  # XDG Desktop Portals (used for wayland screen sharing, file pickers, etc.)
   xdg.portal = {
     enable = true;
     wlr.enable = true;
+    extraPortals = [ pkgs.xdg-desktop-portal-gtk ];
+    config = {
+      common = {
+        default = [ "wlr" "gtk" ];
+        "org.freedesktop.impl.portal.Settings" = [ "gtk" ];
+        "org.freedesktop.impl.portal.FileChooser" = [ "gtk" ];
+      };
+    };
   };
 
   # Configure keymap

home/modules/gui-apps.nix

@@ -36,13 +36,27 @@
 
   gtk = let
     theme = {
-      name = "Colloid-dark";
+      name = "Colloid-Dark";
       package = pkgs.colloid-gtk-theme;
     };
+    iconTheme = {
+      name = "Papirus-Dark";
+      package = pkgs.papirus-icon-theme;
+    };
   in {
     enable = true;
-    inherit theme;
-    gtk4.theme = theme;
+    inherit theme iconTheme;
+    gtk4 = {
+      inherit theme iconTheme;
+      extraConfig = {
+        gtk-application-prefer-dark-theme = 1;
+        gtk-color-scheme = "prefer-dark";
+      };
+    };
+    gtk3.extraConfig = {
+      gtk-application-prefer-dark-theme = 1;
+      gtk-color-scheme = "prefer-dark";
+    };
   };
 
   xdg.mimeApps = {