fix!: default build.cssMinify to 'esbuild' for SSR (#15637)

Author: sapphi-red

docs/config/build-options.md

@@ -130,7 +130,7 @@ In this case, you need to set `build.cssTarget` to `chrome61` to prevent vite fr
 ## build.cssMinify
 
 - **Type:** `boolean | 'esbuild' | 'lightningcss'`
-- **Default:** the same as [`build.minify`](#build-minify)
+- **Default:** the same as [`build.minify`](#build-minify) for client, `'esbuild'` for SSR
 
 This option allows users to override CSS minification specifically instead of defaulting to `build.minify`, so you can configure minification for JS and CSS separately. Vite uses `esbuild` by default to minify CSS. Set the option to `'lightningcss'` to use [Lightning CSS](https://lightningcss.dev/minification.html) instead. If selected, it can be configured using [`css.lightningcss`](./shared-options.md#css-lightningcss).
 

docs/guide/migration.md

@@ -24,6 +24,8 @@ Vite 6 also introduces a new default value for `json.stringify` which is `'auto'
 
 There are other breaking changes which only affect few users.
 
+- [[#15637] fix!: default `build.cssMinify` to `'esbuild'` for SSR](https://github.com/vitejs/vite/pull/15637)
+  - [`build.cssMinify`](/config/build-options#build-cssminify) is now enabled by default even for SSR builds.
 - [[#18209] refactor!: bump minimal terser version to 5.16.0](https://github.com/vitejs/vite/pull/18209)
   - Minimal supported terser version for [`build.minify: 'terser'`](/config/build-options#build-minify) was bumped to 5.16.0 from 5.4.0.
 - [[#18243] chore(deps)!: migrate `fast-glob` to `tinyglobby`](https://github.com/vitejs/vite/pull/18243)

packages/vite/src/node/build.ts

@@ -369,7 +369,7 @@ export function resolveBuildEnvironmentOptions(
     cssCodeSplit: !raw.lib,
     sourcemap: false,
     rollupOptions: {},
-    minify: raw.ssr ? false : 'esbuild',
+    minify: consumer === 'server' ? false : 'esbuild',
     terserOptions: {},
     write: true,
     emptyOutDir: null,
@@ -434,7 +434,7 @@ export function resolveBuildEnvironmentOptions(
   }
 
   if (resolved.cssMinify == null) {
-    resolved.cssMinify = !!resolved.minify
+    resolved.cssMinify = consumer === 'server' ? 'esbuild' : !!resolved.minify
   }
 
   return resolved