anchor.diff:    validTweaks = [ "nord" "dracula" "black" "rimless" "normal" ];
   
     unknownTweaks = lib.subtractLists validTweaks tweaks;
  -  illegalMix = !(lib.elem "nord" tweaks) && !(lib.elem "dracula" tweaks);
  +  illegalMix = (lib.elem "nord" tweaks) && (lib.elem "dracula" tweaks);
   
  -  assertIllegal = lib.assertMsg illegalMix ''
  +  assertIllegal = lib.assertMsg (!illegalMix) ''
       Tweaks "nord" and "dracula" cannot be mixed. Tweaks: ${toString tweaks}
     '';
   
  
positive.code: 
      export HOME=$(mktemp -d)
  
      mkdir -p $out/share/themes
      bash install.sh -d $out/share/themes -t all \
        ${lib.optionalString (size != "") "-s ${size}"} \
        ${lib.optionalString (tweaks != []) "--tweaks " + builtins.toString tweaks}
  
negative.code: 
  stdenvNoCC.mkDerivation rec {
    pname = "catppuccin-gtk";
    version = "0.2.7";
  
    src = fetchFromGitHub {
      repo = "gtk";
      owner = "catppuccin";
      rev = "v-${version}";
      sha256 = "sha256-oTAfURHMWqlKHk4CNz5cn6vO/7GmQJM2rXXGDz2e+0w=";
    };
  
    nativeBuildInputs = [ gtk3 sassc ];
  
    buildInputs = [ gnome-themes-extra ];
  
  