When optimizing your style rules, the number of bytes should not be your only concern. In fact, it comes secondary to the rendering time of your web page. CSS rules affect the amount of work that is required by the browser to render your page. As such, some rules are more expensive than others. For example, changing the color of an element is cheaper than changing its margin. The reason for this is that a change in color only requires your browser to draw the new pixels. While drawing itself is by no means a cheap operation, changing the margin of an element requires much more effort. Your browser needs to both recalculate the page layout and also draw the changes. Optimizing your page's rendering times is a complex topic, and as such is beyond the scope of this book.

However, we recommend that you take a look at http://csstriggers.com/. This site provides a concise overview of the costs involved when updating a given CSS property.