I [once read](https://apple.stackexchange.com/questions/40835/how-to-force-coloured-display-of-visited-links-in-safari-5) you could force the color of visited links in Safari by adding `a:visited { color: #6611cc !important; }` in the .css file under *Preferences < Advanced*. In this way, it will turn every link you've clicked on purple and by so override the actual web design.

I like the idea but I tried to do so, but TextEdit or Word won't allow me to save the file. It wants to add `.rtf`, `.webdesign` or other extensions behind the .css.   
How can I force to add this to the .css file?