I am batman

pkgs/default.nix

@@ -0,0 +1,7 @@
+{ pkgs, ... }:
+{
+  # SDDM theme packages
+  # These will be overlayed into nixpkgs automatically
+  # Usage: pkgs.sddm-sugar-dark-theme
+  sddm-sugar-dark-theme = pkgs.callPackage ./sddm-themes/sugar-dark.nix { };
+}

pkgs/sddm-themes/sugar-dark.nix

@@ -0,0 +1,27 @@
+{
+  stdenv,
+  fetchFromGitHub,
+}:
+stdenv.mkDerivation rec {
+  pname = "sddm-sugar-dark-theme";
+  version = "ceb2c45";
+  dontBuild = true;
+
+  installPhase = ''
+    mkdir -p $out/share/sddm/themes
+    cp -aR $src $out/share/sddm/themes/sugar-dark
+  '';
+
+  src = fetchFromGitHub {
+    owner = "MarianArlt";
+    repo = "sddm-sugar-dark";
+    rev = "ceb2c455663429be03ba62d9f898c571650ef7fe";
+    sha256 = "0153z1kylbhc9d12nxy9vpn0spxgrhgy36wy37pk6ysq7akaqlvy";
+  };
+
+  meta = {
+    description = "Sugar Dark Theme for SDDM";
+    homepage = "https://github.com/MarianArlt/sddm-sugar-dark";
+    license = "GPL-3.0-or-later";
+  };
+}