This doesn't have anything to do with variables, it's simply adding an opacity value to hex-encoded colours. So `#ffff` (or `#ffffffff`) is the sames as `rgba(2

This doesn't have anything to do with variables, it's simply adding an opacity value to hex-encoded colours. So `#ffff` (or `#ffffffff`) is the sames as `rgba(255, 255, 255, 1)`, and `#ffffff7f` would be `rgba(255, 255, 255, 0.5)`. Until now, if you wanted to assign a colour with opacity, you had to use the `rgba()` format. Now you can just hex-encode it :)