[ehnruiz]

Summary

Fixes #615. The property-name gate (isEmittableProperty in src/core/publisher/classCss.ts) used one pattern for every name, /^-{0,2}[a-zA-Z][a-zA-Z0-9-]*$/. That pattern rejects any custom property containing _ or starting with --_, so the stylesheet importer and the publisher both dropped them, and every var() on them resolved to nothing. Webflow exports generate both forms throughout (--brand---ds_mapped---background--page, --_mapped---button--fill).

• Custom properties (--…) are now checked against /^--[a-zA-Z0-9_-]+$/. Standard property names keep the stricter pattern, and the behavior / -moz-binding denylist still applies to both.
• toKebab now passes custom property names through unchanged. Custom properties are case-sensitive, and --brandColor was emitted as --brand-color, which broke var(--brandColor). I found this while reproducing Publisher drops CSS custom properties with an underscore or a leading --_ (classCss VALID_PROPERTY_RE) #615. It is the same problem (custom property names not emitted as authored), so it is in this PR. Happy to split it out if you prefer.

Impact: an imported site keeps all of its custom properties. In the real 7-page Webflow site behind #615, that is the 186 of 322 design-system variables that were being dropped.

Verification

• bun run build (exit 0)
• bun test on this commit (08041d3): 7040 pass, 0 fail (exit 0) on a quiet machine. An earlier run on a loaded machine had 15 timeouts in MCP, auth, sanitize and language-service tests; those files also passed on their own.
• bun run lint (exit 0)
• Docker/deployment check, if relevant (not relevant)

New tests fail on main and pass here:

• bagToCSS emits --card_bg, --_accent and a Webflow-style name as authored, and keeps --brandColor intact.
• cssToStyleRules keeps the Publisher drops CSS custom properties with an underscore or a leading --_ (classCss VALID_PROPERTY_RE) #615 repro's custom properties, with no warnings.
• Negative cases: --, --has space, --x;y, --a:b, font_size and -_x are still dropped.

Checklist

• Tests cover behavior changes.
• Docs were updated when behavior, config, deployment, or public surfaces changed. No docs change needed: docs/features/html-import.md describes the gate by name, not by pattern.
• No compatibility shim was added for old pre-release behavior.
• No secrets, local databases, uploads, or generated artifacts are included.

[ehnruiz]

@DavidBabinec, three small Site Import fixes found on a real Webflow import: #617 (custom properties with _ or --_ were dropped), #618 (color token var() refs), #620 (font token refs, stacked on #618). All rebased on main with tests. Happy to change anything.