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Chapter 14. Thinking Inside the Box: (Padding, Borders, and Margins)

In Chapter 11, I introduced the box model as one of the fundamental concepts of CSS. According to the box model, every element in a document generates a box to which properties such as width, height, padding, borders, and margins can be applied. You probably already have a feel for how element boxes work, from adding backgrounds to elements. This chapter covers all the box-related properties. Once we’ve covered the basics, we will be ready to move boxes around in Chapter 15.

We’ll begin with an overview of the components of an element box, then take on the box properties from the inside out: content dimensions, padding, borders, and margins.

The Element Box

As we’ve seen, every element in a document, both block-level and inline, generates a rectangular element box. The components of an element box are diagrammed in Figure 14-1. Pay attention to the new terminology—it will be helpful in keeping things straight later in the chapter.

The parts of an element box according to the CSS box model.

Figure 14-1. The parts of an element box according to the CSS box model.

Content area

At the core of the element box is the content itself. In Figure 14-1, the content area is indicated by text in a white box.

Inner edges

The edges of the content area are referred to as ...

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