Web Design in a Nutshell, 3rd Edition

Percentage Values

Percentage values are indicated by a number followed by the percentage sign (%). Percentage values are calculated relative to other values in the document. When specifying percentage values for measurements, it is important to pay attention to how they will be calculated for the given property. Sometimes percentages are relative to the current element. In other instances, they are calculated based on the properties of the parent element. The CSS Recommendation specifies how percentage values are calculated for each value, and there are notes provided in the descriptions in this book as necessary.