I am trying to create a derivation for the flat-remix-icon-theme and need some help. My derivation seems to build and install, however I am not able to select the new icon theme in gnome tweaks. The derivation is

{ stdenv, fetchFromGitHub, gtk3 }:

stdenv.mkDerivation rec {
  name = "${package-name}-${version}";
  package-name = "flat-remix-icon-theme";
  version = "2019-02-14";

  src = fetchFromGitHub {
    owner = "daniruiz";
    repo = "flat-remix";
    rev = "c2503f5b8104bbf6f7879260b3a6e4736ff239a5";
    sha256 = "1ghl03zmqrhg7d61vq56p9n9bgmbv0023fmf5m46p8i6xc1fljvz";

  nativeBuildInputs = [ gtk3 ];

  installPhase = ''
    mkdir -p $out/share/icons
    mv Flat-Remix* $out/share/icons/

  postFixup = ''
    for theme in $out/share/icons/*; do
      gtk-update-icon-cache $theme

  meta = with stdenv.lib; {
    description = "Flat remix is a pretty simple icon theme inspired on material design.";
    homepage = https://drasite.com/flat-remix;
    license = with licenses; [ gpl3 ];
    platforms = platforms.all;
    maintainers = with maintainers; [ mschneider ];

Note, I am not in maintainer-list.nix yet. I ran nix-build -A flat-remix-icon-theme which built the result.

Any suggestions?

I ran nix-build -A flat-remix-icon-theme which built the result.

And it didn’t affect your current system or user profile, as designed. I suppose you should install it into your system or user profile, e.g., add it to environment.systemPackages and nixos-rebuild test? This way it should end up in /var/run/current-system/sw/share/themes/ and your theme picker should pick it up.

Thanks. That was the problem.