The computed value of a CSS property is the value that is transferred from parent to child during inheritance. It is calculated from the specified value by:
- Handling the special values
inherit,initial,revert,revert-layer, andunset. - Doing the computation needed to reach the value described in the "Computed value" line in the property's definition table.
The computation needed to reach a property's computed value typically involves converting relative values (such as those in em units or percentages) to absolute values. For example, if an element has specified values font-size: 16px and padding-top: 2em, then the computed value of padding-top is 32px (double the font size).
However, for some properties (those where percentages are relative to something that may require layout to determine, such as width, margin-right, text-indent, and top), percentage-specified values turn into percentage-computed values. Additionally, unitless numbers specified on the line-height property become the computed value, as specified. The relative values that remain in the computed value become absolute when the used value is determined.
Note: The getComputedStyle() DOM API returns the resolved value, which may either be the computed value or the used value, depending on the property.