A GTK, xfwm4, openbox-3, and GNOME-Shell - Dark Mode Theme - Plata-Dark-Arc is a new Gtk+ theme based on a prudent blend of the latest Material Design refresh and 2019's top-rated theme, Arc.
Plata-Dark-Arc mixes Blackened-Steel, indigo, and shades of gray with bits of royal-blue, and violet. Plata-Dark-Arc supports Gtk+ 3x, as well as Gtk+ 2, and a multitude of desktop environments like Gnome (and Flashback), Xfce, Mate, LXDE, Openbox, and Cinnamon.
Manual Installation Is Easy:
1) Extract the "tar.xz" file into your "~/.themes/" folder - to install for current user only - or into the "/usr/share/themes/" folder - for the theme to be applied globally. 2) Use the GNOME Tweak Tool or an equivalent app to enable it for your desktop.
If installing manually, make sure to install the dependency: "Murrine theme engine" if you do not already have it; and update your GTK+packages if you have not.