Stormy, you won't be able to edit the CSS from inside the admin panel. You'll need to use a FTP client to do that.
Also, if you're starting fresh with a new Magento store I would HIGHLY RECOMMEND creating your own theme copy to work from. The easiest way to do this is to copy all the files from one of the existing Magento themes ("Modern, for example"), rename it and then modify as you wish. Then, if you mess something up you have the original theme underneath to default to simply by removing the problematic file.
For more info on creating a new theme, check out this post on the Magento site: