This is the Ambiance Crunchy fluxbox theme !
It's inspired by the Ambiance theme of Ubuntu with 4 flavours (colors of selection) and 2 sets of buttons (rounded and squared). The source files and the scripts are available in themes/00-Customizations/fluxbox.
The theme is now closer to its versions on other desktops.
NEW: set of grub2 themes. More infos : https://www.gnome-look.org/p/1160963/
* open a Terminal in the folder where the file Crunchy-themes.tar.gz is
* and type the command (Ubuntu/Debian like distros):
sudo tar -zxvf Crunchy-themes.tar.gz -C /usr/share