I accidently removed Default folder from /usr/share/themes and now can not change the Keybindig theme back to default under advanced setting -> theme. Default option is simply gone, not there anymore. Couldn't get it back... I am using Ubuntu 12.04 with Gnome shell. Any thoughts on what can bring this option back? Thanks!
Open a terminal and enter
The command shows you which packages use (and create) this directory. In my case the output is:
So they create the directory and fill it with the correct content.
I better not ask how and why did you delete it, but anyways, probably you could:
1: reinstall system (aka: upgrade to the same version)
2: get the /usr/share folder from another installation, or from the liveCD/DVD
3: create the folder, and add a new theme
Hope that helps, good luck! Cheers!