Status of this document 1. Introduction
The [css-variables-1] specification defined the concept of "cascading variables", author-defined variables created from the value of custom properties, capable of being substituted into arbitrary other properties via the var() function.
This specification defines a related, but simpler, concept of environment variables. Unlike "cascading variables", which can change thruout the page as their corresponding custom property takes on different values, an environment variable is "global" to a particular document—its value is the same everywhere. The env() function can then be used to substitute the value into arbitrary locations, similar to the
... read the whole story at drafts.csswg.org.