help with CSS

If I am writing this question in the wrong forum then I am sorry. I have been trying to change my background color and when I go int general css it tells me that it is not writeable?!? I don't understand what is going on with it. Please if you can help me that would be great. Is it the software I bought? I can't figure this out.

Thanks in Advance

The css files are write protected. Using an ftp program you will need to log onto your server and change permissions i.e. 644 to 666 and 755 to 777. Make sure you change them back again afterwards!