How to apply Clearlooks-Phenix to window title bars on Ubuntu 15.10 and 16.04

(For Clearlooks-Phenix users)

On Ubuntu 15.10 and 16.04, gnome-tweak-tool doesn’t provide the item for window theme selection.  Alternatively, you can apply Clearlooks-Phenix theme to window title bars in GNOME3 flashback sessions (for both metacity and compiz) by typing:

$ gsettings set org.gnome.metacity theme Clearlooks-Phenix