Add system theme switch script

system/specialisation.nix

@@ -0,0 +1,24 @@
+{ pkgs, ... }: {
+  specialisation.dark-theme.configuration = {
+    nixpkgs.overlays = [
+      (final: prev: {
+        uservars = prev.uservars;
+      })
+    ];
+  };
+  specialisation.light-theme.configuration = {
+    nixpkgs.overlays = [
+      (final: prev: {
+        uservars = prev.uservars // rec {
+          theme = prev.uservars.themes.light;
+          color = theme.color;
+        };
+      })
+    ];
+  };
+  environment.systemPackages = [
+    (pkgs.writeShellScriptBin "theme" ''
+      sudo "/nix/var/nix/profiles/system/specialisation/$1-theme/bin/switch-to-configuration" test
+    '')
+  ];
+}