OK, first things first: Don't input commands you don' t understand what they do.
sudo apt-get autoremove --purge light-themes sudo apt-get install light-themes
If you had Cairo dock installed and then removed it, the only thing that should've been removed was Cairo Dock. The themes and the icons have nothing to do with it.
So what you did was to remove the dependencies that Cairo dock installed and uninstall the themes along with them, which you shouldn't have done in the first place. And by the way, that command does not remove Cairo Dock.
Now, your question confuses me a lot. You removed Cairo, then changed the Theme back to Ambience (Ubuntu's default)? or what did you do?. Afterwards the theme didn't change (it wasn't the correct command to do that) and the Font looks weird (screenshot required).
Moreover your alt+tab issue must have been caused by something you *removed with the command.
To change Themes you have to install
gnome-tweak-tool that'll change the themes, icons, fonts, etc.
To reset Unity settings use
Reinstall the Ubuntu Desktop package
sudo apt-get install ubuntu-desktop