The fastest way to identify and "tweak" css declarations is to use the Firefox browser and its FIREBUG plugin.

This tool allows you to display a webpage and then do "off-line" analysis and editing. It will (amongst other functions) reveal the style ID and CLASS of any displayed element, and the declarations currently associated with it.

You can then apply an 0ffline edit to the css, and see the result real-time on screen.

All you need then do is commit the changes you made, to the LIVE stylesheet(s).