2.3. Class and ID Selectors

So far, we've been grouping selectors and declarations together in a variety of ways, but the selectors we've been using are still simple ones. The selectors we've used refer only to document elements; they're fine up to a point, but there are times when you need something a little more specialized.

In addition to raw document elements, there are two other types of selectors: class selectors and ID selectors, which let you assign styles in a way that is independent of document elements. These selectors can be used on their own or in conjunction with element selectors. However, they work only if you've marked up your document appropriately, so using them generally involves a little forethought and planning.