As a normal nix user you can install the Oxygen GTK theme: $ nix-env -i oxygen-gtk KDE will run any scripts you place in ~/.kde/env on startup so this is a good place to set the GTK_PATH so that applications can find the theme engine. If the path is wrong/unset you will see errors like this: Gtk-WARNING **: Unable to locate theme engine in module_path To set Oxygen-GTK as the gtk theme create the following file and make it executable: ~/.kde/env/set-gtk-theme.sh #!/bin/sh export GTK_PATH=$GTK_PATH:~/.nix-profile/lib/gtk-2.0 export GTK2_RC_FILES=$GTK2_RC_FILES:~/.nix-profile/share/themes/oxygen-gtk/gtk-2.0/gtkrc |