2.1.6 [CSS3Color:2011] Section 4.2.4, HSL color values
HSL colors are encoding as a triple (hue, saturation, lightness). Hue is represented as an angle of the color circle (i.e. the rainbow represented in a circle). This angle is so typically measured in degrees that the unit is implicit in CSS; syntactically, only a <number> is given.
Quirks Mode, IE7 Mode, and IE8 Mode (All Versions)
HSL color values are not supported.