I have answered several questions today that involved looking at either the css styles or html markup on the sites in question.
For anyone who is not aware, I’m sure all browsers do this or have a plugin for it, but I use Firefox and it allows me to CTRL-click on a page and click from object to object to see the cascade of css on a specific object as well as the html structure which helps me find ids and classes to target for writing the css.
I strongly suggest anyone who is not doing this should find it on your browser or download a plugin. I have saved countless hours by being able to inspect a rendered page quickly and easily. This is even more important now when most of the pre-code we see is php.
Anyone who has specific information on doing this with various browsers may want to post that info under this header.
Hope this helps.