4.7 [CSS-Level1-2008] Section 5.5.24, height
The [CSS-Level1-2008] specification states:
Section 5.5.24: Height Value: <length> | auto Initial: auto Applies to: block-level and replaced elements Inherited: no Percentage values: N/A
IE7 Mode, IE8 Mode, and IE9 Mode (All Versions)
The percentage height is calculated according to the [CSS-Level2-2009] specification, which allows for percentage values.