The format of a percentage value is a number (with or without a decimal point) immediately followed by '%'. Percentage values are always relative to a length unit. Each property that allows percentage units also define what length unit they refer to. Most often this is the font size of the element itself:

For example :

P { line-height: 120% }

120% of the element's 'font-size'

Child elements inherit the resultant value, not the percentage value.

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