Summary

Validates CSS custom property values as raw CSS token streams before saving/parsing them.

This prevents malformed values like #sd' from being normalized into sd or serialized into broken canvas CSS that invalidates the whole generated rule.

Changes

• Added tokenizer-based validation for custom property values.
• Rejects malformed strings, URLs, comments, unmatched blocks, and trailing backslashes.
• Preserves raw custom property declaration values before css-tree can repair/normalize them.
• Prevents custom property value editing from coercing invalid input through fallback parsing like kebabCase() or color recovery.
• Added regression tests for advanced panel input and CSS data parsing.

Verification

• pnpm --filter @webstudio-is/css-data test -- parse-css-value.test.ts parse-css.test.ts
• pnpm --filter @webstudio-is/builder test -- parse-intermediate-or-invalid-value.test.ts parse-style-input.test.ts