Web Design in a Nutshell, 3rd Edition

Line Height

In CSS, the line-height property defines the minimum distance between the baselines of adjacent lines of text. A baseline is the imaginary line upon which the bottoms of characters sit. Line height is analogous to leading or interlinear space (the amount of space between lines) in traditional typesetting. Adjusting the line height can change the color of a block of text. In this case “color” refers not to hue (like blue or green), but rather the overall density or darkness of the text.

This section looks at both the line-height property and the method by which CSS calculates the actual height of lines. CSS line height handling has an impact on vertical alignment within text, discussed later.