2.1.2 [W3C-CSS3-Color] Section 3.2, Transparency: the ‘opacity’ property
The specification states:
Name: opacity Value: <alphavalue> | inherit Initial: 1 Applies to: all elements Inherited: no Percentages: N/A Media: visual Computed value: The same as the specified value after clipping the <alphavalue> to the range [0.0,1.0].
Quirks Mode, IE7 Mode, and IE8 Mode (All Versions)
The opacity property is not supported.