How to edit live theme .info file (localhost)
May be the problem is of / present at the starting in your first attempt(/css/main.css), try once with:

stylesheets[all][] = css/main.css


Note: Clear the cache and check if it works.

Also you can check the following links if it helps:
https://drupal.org/node/171205
https://drupal.org/node/171209