Style properties are a good place to start. They are defined into sections, so at least you know the general area of where you are trying to change what. If you really want to delve deep into it, use Firebug or Developer Tools in Chrome, inspect whatever element you want to change, then search for the class in templates, then see if there is an @property in the rule. Then you know exactly what property (more or less) controls the appereance of what you want to change.
