I wanted to see what my form would look like without the included styles turned off, so I checked "Don't use default CSS" and saved the Clean Contact settings. I didn't like the resulting look, and was too lazy to write my own CSS for it, so I toggled the checkbox off and saved the settings again.
Now my contact form only appears as an empty pink box.
I'll probably have to uninstall and reinstall the plugin, I imagine.
Please fix it if you can, developer, because I'd like to use this for client sites. A simple contact form with Akismet filtering is the answer to so many problems.