I have been used Ubuntu for 1+ years. Since I was a old MacOS user, and I wanted to use Ubuntu easily, I installed and configured a MacOS-ish theme:

Well, I am kinda tired of it.

Let's revert it with only one command:

dconf reset -f /

This command won't delete any of your user files, and is really useful for whom have crashed their desktops or have other desktop-related problems.