问题
Inspired by this question, I realized I haven't been able to find a clear answer to what the bit depth of the a part of rgba and hsla in CSS3 colors actually is. I've hunted through various W3C documentation, but aside from specifying that alpha is represented as a float range 0.0% - 100.0%, and the definition for the bit depth of the alpha channel in PNGs, I don't really have a clear picture (haha) of what the limits of the alpha channel in CSS3 actually are. Can someone find something more normative?
来源：https://stackoverflow.com/questions/16503485/what-is-the-bit-depth-of-the-alpha-channel-in-css3-colors