{
  description = "Firefox userChrome.css";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs =
    {
      self,
      nixpkgs,
      flake-utils,
    }:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in
      {
        packages.default = pkgs.stdenvNoCC.mkDerivation {
          pname = "firefox-userchrome";
          version = "1.0.0";
          src = ./.;
          dontBuild = true;
          installPhase = ''
            mkdir -p $out/chrome
            cp userChrome.css $out/chrome/userChrome.css
          '';
        };

        # `nix fmt` formats userChrome.css with prettier
        formatter = pkgs.writeShellApplication {
          name = "fmt";
          runtimeInputs = [ pkgs.nodePackages.prettier ];
          text = ''
            prettier --write "$@"
          '';
        };
      }
    );
}