{ config, lib, ... }: let
  inherit (lib) mkIf;
in {
  config = mkIf config.isDesktopNotWsl {
    # Specialisations for system-level theme switching.
    specialisation = {
      dark-theme = {
        configuration = {
          # Force dark theme.
          themeOverride = lib.mkForce true;
          # For identification.
          system.nixos.tags = [ "dark-theme" ];
          # Include the light theme specialisation in dark theme.
          specialisation.light-theme = {
            configuration = {
              themeOverride = lib.mkForce false;
              system.nixos.tags = [ "light-theme" ];
            };
          };
        };
      };
      # Light theme specialisation.
      light-theme = {
        configuration = {
          # Force light theme.
          themeOverride = lib.mkForce false;
          # For identification.
          system.nixos.tags = [ "light-theme" ];
          # Include the dark theme specialisation in light theme.
          specialisation.dark-theme = {
            configuration = {
              themeOverride = lib.mkForce true;
              system.nixos.tags = [ "dark-theme" ];
            };
          };
        };
      };
    };
    # Home Manager specialisations for user-level theme switching.
    home-manager.sharedModules = [{
      specialisation = {
        dark = {
          configuration = {
            # Override theme to dark in home-manager.
            home.sessionVariables.THEME_MODE = "dark";
          };
        };
        light = {
          configuration = {
            # Override theme to light in home-manager.
            home.sessionVariables.THEME_MODE = "light";
          };
        };
      };
    }];
  };
}

  # Global theme configuration - can be overridden by specialisations.
  is_dark = if config.themeOverride != null
           then config.themeOverride
           else false;  # Default to light.

  # Global theme configuration - use `tt dark` or `tt light` to switch.
  is_dark = true;

    vivid.dark      = "gruvbox-dark-hard";
    vivid.light     = "gruvbox-light-hard";

    nvim.dark       = "gruvbox-material";
    nvim.light      = "gruvbox-material";
    alacritty.dark  = "gruvbox_material_hard_dark";
    alacritty.light = "gruvbox_material_hard_light";
    zellij.dark     = "gruvbox-dark";
    zellij.light    = "gruvbox-light";
    starship.dark   = "dark_theme";
    starship.light  = "light_theme";
    vivid.dark      = "gruvbox-dark";
    vivid.light     = "gruvbox-light";

      name    = "Adwaita-dark";

      name = "Adwaita-dark";

      name    = "Adwaita";

      name = "Adwaita";

  # Helpers.

  # helpers

  };
  # Separate option for specialisation override.
  options.themeOverride = mkOption {
    type = types.nullOr types.bool;
    default = null;
    description = "Force dark or light theme (used by specialisations)";

    nvim      = get_theme "nvim";
    alacritty = get_theme "alacritty";
    zellij    = get_theme "zellij";
    starship  = get_theme "starship";

  # Export theme info as environment variable.
  config.environment.variables.THEME_MODE        = variant;
  config.environment.sessionVariables.THEME_MODE = variant;

  # Export theme info as env var.
  config.environment.variables.THEME_MODE = variant;