Biome's CSS parser rejects Tailwind v4 directives (@custom-variant, @theme) by default

In a Tailwind v4 project, Biome's CSS parser treats directives like @custom-variant pointer-fine (@media (pointer: fine)) and @theme as syntax errors with the message "Tailwind-specific syntax is disabled." The error is fatal: the formatter aborts, so biome check exits non-zero on the affected CSS file. Fix is to enable the parser option in biome.json: "css": { "parser": { "tailwindDirectives": true } }. The biome diagnostic itself mentions this option, but it's easy to miss when first wiring biome into a Tailwind project. Verified 2026-05-01 with @biomejs/biome 2.4.13 and tailwindcss 4.x.

When wiring Biome into a project that uses Tailwind CSS v4 (or any CSS with non-standard at-rules), set "css": { "parser": { "tailwindDirectives": true } } in biome.json. Verify current schema options at https://biomejs.dev/reference/configuration/.