Summary

Rolldown has completely removed native CSS support. This implements the full CSS pipeline as a Rolldown plugin, following Vite's cssPlugin pattern.

• CssPlugin: Single plugin replacing both LightningCSSPlugin and CssCodeSplitPlugin — handles CSS loading, preprocessing, collection per chunk, and asset emission
• Preprocessor support: Sass/Less/Stylus compilation with URL rebasing for imported files from different directories
• Direct Lightning CSS: Replace unplugin-lightningcss with direct lightningcss.transform() API for CSS syntax lowering
• CSS code splitting: Per-chunk CSS assets (splitting mode) or merged single CSS file (non-splitting mode)
• Expanded CssOptions: Added preprocessorOptions (scss/sass/less/styl/stylus) and lightningcss configuration

Architecture

JS imports ./style.css or ./style.scss
  → load hook: read file, compile preprocessor, Lightning CSS lowering,
    store in styles map, return { code: '', moduleSideEffects: 'no-treeshake' }
  → renderChunk: collect CSS per chunk, emit .css assets or accumulate
  → generateBundle: merge all CSS into single file (non-splitting mode)

Related Issues