[css-scoping] Expose counter values for use as variable values

[jp-crane]

What is the problem?
Currently, CSS counters can only be accessed via the content property and related counter functions. It is not possible to use the value of a counter in other CSS properties (e.g., as a number in calc(), or assign it to a custom property for use elsewhere).

Why is this useful?
This would allow for more powerful, context-aware styling in trees, outlines, and other structured content, such as indenting, coloring, or sizing based on counter values.

Proposed solution:
Expose CSS counter values as variables or allow their use in property value calculations (e.g., margin-left: calc(counter(depth) * 1em); or --depth: counter(depth);).

References:
CSS Counters Module Level 3
CSS Variables

[jfkthame]

There's some prior discussion in #1026 that you might like to review.

[jp-crane]

Ah thanks -- I looked back a couple years for duplicates but clearly didn't go far enough.

[bramus]

Duplicate. Closing.