When you make changes to your CSS file, you need to view the changes in your browser. The browser will often store the most recent information in its "cache" and when you hit Refresh, it will show you the stored information and not the new one.
You can clear the "cache" in order to see the new changes by:
MSIE: Hold down SHIFT and click on the REFRESH button in the toolbar under the menu.
FireFox: Hold down CNTRL+SHIFT+R.
MSIE - Serious clearing: If you are having problems clearing out the cache, then force it by choosing from the menu TOOLS > INTERNET OPTIONS and looking for Temporary Files. Click on Delete Temporary Files. You can or not choose the checkbox, I usually don't, to delete all Internet files, as that will also clear all your passwords and cookies, but if you are having trouble, this is a way to do it.
How about some other browsers? How do you clear the cache from Safari, Opera, etc.?