Zephyr is a dark pastel GTK theme built for Xfce, based on Breeze Dark
Just clone the repository into your ~/.themes directory:
mkdir -p ~/.themes cd ~/.themes git clone --depth=1 https://github.com/Alanaktion/zephyr-gtk.git zephyr
If you don't have Git installed, try this instead:
mkdir -p ~/.themes cd ~/.themes wget https://github.com/Alanaktion/zephyr-gtk/archive/master.zip mv zephyr-gtk-master zephyr unzip master.zip rm master.zip
If you need a global installation, put Zephyr in /usr/share/themes/ instead. Be sure to set the permissions correctly if you do, otherwise it may not work correctly for all users and applications.
Zephyr is built as a conversion script from Breeze Dark GTK, and a custom Xwfm theme. If you want to build it yourself, start with Breeze Dark and run the Zephyr convert.sh script, which recolors the PNG images, generates the Xfwm button pixmaps, and swaps out colors in the GTK theme files.
Contributions to Zephyr are welcome, but should typically only change the convert.sh script or the xfwm directory to avoid being overwritten by the conversion script. Take a look at the open issues to see what needs to be worked on and what feature requests exist, or just do your own thing and add something neat!