I've never met a person yet that installed a theme and was ready to launch their Magento store without wanting or even needing changes made to the store design. It's natural, as a store needs to have its own personality and its own brand. In this section, we hope to uncover many of the mysteries of how Magento controls a store's look and feel through layered components that, once you understand how they work together, will give you a tremendous ability to make your Magento store a unique, productive online retail destination.
Finding CSS
While you can view the source code of a webpage in any browser, there are better ways of identifying not only the HTML elements of a page, but the exact CSS style(s) that are controlling how that component appears.
For Firefox browsers, you can install the Firebug plugin (http://getfirebug.com). For Safari and Chrome users, this functionality is included with the browser. Another great tool for Firefox users is the Web developer add-on (https://addons.mozilla.org/pt-br/firefox/addon/web-developer/). These tools allow you to select an element on the page and view in another window, what the styling rules are that apply to the element. Once you know that, you can easily find the CSS style statement in the theme's CSS stylesheets and make any changes you wish.