[css-env-1] environment variables as redundant mechanism

[srsgores]

After reading the proposal spec on CSS environment variables, I find the proposed env keyword redundant and misleading:

1. Introduces a new function which essentially does the same thing as var()
2. Lacks a clear specificity on how var() plays with env()
3. Adds another level of complexity to CSS for new learners which may impede or slow down learning

Instead, I propose using the familiar var keyword already available. UAs can predefine custom properties to known variable names. It seems to me that the draft tries to solve a problem that really isn't there for most authors.

For fallbacks, the author may define those using the normal :root or specificity.

Instead of focusing on creating a new function, let's focus on a naming convention for UAs to follow that standardizes the variable names we can use.

[Loirooriol]

See #3285, env() is more like calc() or attr() rather than var().

[tabatkins]

Yup, env() serves a different purpose from var(), tho the two are roughly similar.