Dave's right - it will help you loads in the future to keep an eye of the CSS Styles panel for the info you need (and a quick way to change it).
Having selected any element in the page's form, you can also right-click on any style in the CSS Styles panel, or right click on the 'About' info bar just below the 'Current' styles, and select 'Go to Code'.
This will open the stylesheet in 'split' view. (The name of the stylesheet will be highlighted in the associated files bar too).