[Review] CSS: --ds-* naming, context blocks, cascade layers, delivery, linting

Problem/Motivation

Everything the contract delivers is CSS: --ds-* custom properties in a cascade layer, with blocks for dark mode and more contrast. Module CSS must use them and logical properties, enforced by two stylelint rules.

The full brief, with what we built, screenshots and how to try it in the demo site: https://project.pages.drupalcode.org/design_system_api/reviews/css/

Questions

1. Is --ds- with a group-element-role-state grammar acceptable for a shared vocabulary?
2. Context blocks instead of light-dark(): do you agree with the trade-off?
3. Should Drupal define a cascade layer order, and where would this layer go?
4. Linked file, library, inline or aggregate: how should the values be delivered?
5. Are the two lint rules the right minimum, and should they move to core's config?

Short answers help as much as long reviews ("2: no, because …"). Each question in the brief links to the part of the concept it affects.

Proposed resolution

Collect answers here. Settled answers become decisions, change the concept, and are summarized under "What we heard" in the brief.

Remaining tasks

• Review by maintainers of this area.
• Summarize the outcome in the brief.

Proposing changes to the brief

The brief is docs/reviews/css.md in this repository: open a merge request from this issue's fork.