This chapter began with a discussion of the tools you will need to begin working on your themes in earnest. The Devel module and the Theme Developer module are two of the key tools you will want to have at your disposal.
We learned to manage the customization of an existing theme. In this chapter we dealt for the first time with one of the most powerful techniques available to themers the use of sub-themes. Through the implementation of a sub-theme, the themer is able to leverage the power of an existing base theme while retaining the flexibility needed to customize virtually every element of the styling and the structure.
This chapter showed how to create a sub-theme and then how to implement various common approaches to customizing that sub-theme. In the next chapter we look at how you can create a completely new theme for your Drupal 7 site.