These are very useful tools for you to trace the html code to find out the classes of element, in order to customize your design.
For FF:
Firebug:
download link: https://addons.mozilla.org/zh-TW/firefox/addon/1843
For IE:
Internet Explorer Web Developer Tools
download link: http://www.microsoft.com/downloads/details.aspx?FamilyID=E59C3964-672D-4511-BB3E-2D5E1DB91038&displaylang=en
