Modern CSS

Opinionated rules for modern CSS, so agents and people write it consistently.

These rules sit on top of the Modern Web Guidance skill, which must be installed. It explains what each feature does, when it applies, and how to fall back. It leaves choices open: which color space, whether to scope, when to nest, how to size type. These rules settle them; retrieve its guides for everything else. Where the two disagree, the rule wins.

The stylelint-config-modern package enforces every rule a linter can. This skill gets agents writing those from the start, and carries the rest.

Browser support policy: features within Baseline Newly Available are used natively, without @supports fallbacks, as progressive enhancement.

Rules

Architecture

Organizing styles (@layer)