Computer GUIs frequently include "three-dimensional-looking" elements, which are achieved by using colors differing only in brightness for the fringes of objects. CSS has predefined border thingies to make this easier, but they don't always render as you might like.
This paragraph is inset; it has to be particularly dark to be darker than the "light" side of its bevel.
This paragraph is beveled by hand, simply by specifying colors for the borders and interior.
This paragraph is grooved by hand, by putting it inside a manually inset <div> and then beveling the paragraph by hand. Doing this with a real paragraph requires overriding the normal top and bottom margins that paragraphs get.