Materia (formerly Flat-Plat) is a Material Design theme for GNOME/GTK+
based desktop environments. It supports GTK+ 3, GTK+ 2, GNOME Shell,
Budgie, Cinnamon, MATE, Unity, LightDM, GDM, Chrome theme, etc.

Note: this is not the latest version but the last one supporting
      GTK+ 3.18 and therefore suitable for Slackware 14.2