use flake for unstable packages

flake.nix

@@ -1,6 +1,7 @@
 {
   inputs = {
     nixpkgs.url = "nixpkgs/nixos-22.11";
+    nixpkgs-unstable.url = "nixpkgs/nixos-unstable";
     # hyprland.url = "github:hyprwm/Hyprland";
     supercolor.url = github:zoe-bat/supercolor;
     kaokao.url = github:zoe-bat/kaokao;
@@ -12,17 +13,27 @@
   outputs =
     { self
     , nixpkgs
-    # , hyprland
+      # , hyprland
     , home-manager
     , supercolor
+    , nixpkgs-unstable
     , kaokao
-    }@inputs: {
+    }@inputs:
+    let 
+      system = "x86_64-linux";
+      overlay-unstable = final: prev: {
+        unstable = import nixpkgs-unstable {
+          inherit system;
+          config.allowUnfree = true;
+        };
+      };
+    in
+    {
       nixosConfigurations.bat = nixpkgs.lib.nixosSystem {
         system = "x86_64-linux";
         modules = [
+          ({ config, pkgs, ... }: { nixpkgs.overlays = [ overlay-unstable ]; })
           ./configuration.nix
-          # hyprland.nixosModules.default
-          # { programs.hyprland.enable = true; }
         ];
         specialArgs = inputs;
       };

i3/config.nix

@@ -116,13 +116,11 @@ in
         j = "exec /etc/nixos/i3/brightness.py 100-";
       };
       media = {
-        Return = "mode default";
         Escape = "mode default";
         j = "exec --no-startup-id python3 /etc/nixos/i3/volume.py 5%-";
         k = "exec --no-startup-id python3 /etc/nixos/i3/volume.py 5%+";
         m = "exec --no-startup-id amixer set Master toggle";
-        c = "exec --no-startup-id kitty cmus";
-        v = "exec --no-startup-id mpv";
+        n = "exec --no-startup-id amixer set Capture toggle";
         space = "exec python3 /etc/nixos/i3/play_pause.py";
       };
     };

user.nix

@@ -1,10 +1,4 @@
 { pkgs, users, config, inputs, supercolor, kaokao, ... }:
-let
-  unstable = import
-    (builtins.fetchTarball https://github.com/nixos/nixpkgs/tarball/master)
-    # reuse the current configuration
-    { config = config.nixpkgs.config; };
-in
 {
   # Define a user account. Don't forget to set a password with ‘passwd’.
   users.users.zoe = {