Skin design
Installation and Configuration
Im not sure about the code in relation to the question, just trying to make sure steps to edit the .css file are appearing in your site after you upload them, so..
What you have there are 2 separate systems, the STYLE tab in the ACP and the upload the .css file. If possible I would recommend using just one or the other rather than mixing them. My preference is for the .css files because you have more control.
The way the STYLE tab works is it stores extra CSS in the database that is applied after all the .css files have been processed, so it gets the final word. It also uses the !important tag a lot so if its defined as a rule there, then no changes to the .css files are going to make any difference while there is a STYLE tab rule defined for the same thing.