Although some aspects of the CSS formatting model may seem counterintuitive at first, they begin to make sense the more one works with them. In many cases, rules that seem nonsensical or even idiotic turn out to exist in order to prevent bizarre or otherwise undesirable document displays. Block-level elements are in many ways easy to understand, and affecting their layout is typically a simple task. Inline elements, on the other hand, can be trickier to manage, as a number of factors come into play, not least of which is whether the element is replaced or nonreplaced. Now that we've established the underpinnings of document layout, let's turn our attention to seeing how the various layout properties are used. This effort will span several chapters, and we'll start with the most common box properties: padding, borders, and margins.