fix: add cssMinify: false to all Vite configs to prevent light-dark() breakage - #623
Merged
Merged
Conversation
… breakage LightningCSS lowers CSS light-dark() into polyfill variables (--lightningcss-light/--lightningcss-dark) that are never initialized, silently breaking all XDS theming colors. This has bitten us 3 separate times (PRs #558, #566, #499) across different Vite configs. Changes: - apps/example-vite/vite.config.ts: add build.cssMinify: false - apps/storybook/vite.config.ts: add build.cssMinify: false - apps/example-vite/README.md: add lightningcss gotcha as top entry, detailed explanation section, and update inline config example - apps/example-nextjs/README.md: add awareness note (Next.js uses PostCSS so not directly affected, but warn about custom minifiers) Co-authored-by: Navi <navi@navibot.dev>
meta-cla
Bot
added
the
CLA Signed
Contributor
PR Analysis Report📚 Storybook PreviewView Storybook for this PR 🧪 Sandbox PreviewView Sandbox for this PR No new or modified components detected. Bundle Size Summary
Accessibility AuditStatus: No accessibility violations detected. Generated by PR Enrichment workflow | Storybook | Sandbox | View full report |
cixzhang
added a commit
that referenced
this pull request
Mar 15, 2026
LightningCSS lowers light-dark() into --lightningcss-light/--lightningcss-dark polyfill variables for older browsers. This polyfill actually works correctly IF the color-scheme declaration is in the same CSS file — lightningcss injects toggle variable initialization wherever it sees color-scheme. But when light-dark() and color-scheme are in separate files (as with XDS, where tokens are in xds.css but color-scheme is set by XDSTheme via StyleX), the polyfill vars are used but never defined, breaking all colors. Fix: include `color-scheme: light dark` in both xds.css and theme CSS output so the polyfill is self-contained. This makes XDS CSS compatible with any bundler that runs lightningcss regardless of target configuration. This reverts the cssMinify: false workarounds from PR #623 and earlier (PRs #558, #566) since they're no longer needed — the root cause is fixed. Co-authored-by: Navi <navi@navibot.dev>
cixzhang
added a commit
that referenced
this pull request
Mar 15, 2026
LightningCSS lowers light-dark() into --lightningcss-light/--lightningcss-dark polyfill variables for older browsers. This polyfill actually works correctly IF the color-scheme declaration is in the same CSS file — lightningcss injects toggle variable initialization wherever it sees color-scheme. But when light-dark() and color-scheme are in separate files (as with XDS, where tokens are in xds.css but color-scheme is set by XDSTheme via StyleX), the polyfill vars are used but never defined, breaking all colors. Fix: add `color-scheme: light dark` to: - reset.css — on :where(html), the canonical place for the declaration. Every XDS app imports this first. - build-css.mjs output (xds.css) — for consumers who import xds.css without reset.css - build-theme.mjs output (theme.css) — for theme files containing light-dark() values This makes XDS CSS compatible with any bundler that runs lightningcss regardless of target configuration. Reverts the cssMinify: false workarounds from PR #623 and earlier (PRs #558, #566). Co-authored-by: Navi <navi@navibot.dev>
cixzhang
added a commit
that referenced
this pull request
Mar 15, 2026
LightningCSS lowers light-dark() into --lightningcss-light/--lightningcss-dark polyfill variables for older browsers. This polyfill actually works correctly IF the color-scheme declaration is in the same CSS file — lightningcss injects toggle variable initialization wherever it sees color-scheme. But when light-dark() and color-scheme are in separate files (as with XDS, where tokens are in xds.css but color-scheme is set by XDSTheme via StyleX), the polyfill vars are used but never defined, breaking all colors. Fix: add `color-scheme: light dark` to: - reset.css — on :where(html), the canonical place for the declaration. Every XDS app imports this first. - build-css.mjs output (xds.css) — for consumers who import xds.css without reset.css - build-theme.mjs output (theme.css) — for theme files containing light-dark() values This makes XDS CSS compatible with any bundler that runs lightningcss regardless of target configuration. Reverts the cssMinify: false workarounds from PR #623 and earlier (PRs #558, #566). Co-authored-by: Navi <navi@navibot.dev>
cixzhang
added a commit
that referenced
this pull request
Mar 15, 2026
LightningCSS lowers light-dark() into --lightningcss-light/--lightningcss-dark polyfill variables for older browsers. This polyfill actually works correctly IF the color-scheme declaration is in the same CSS file — lightningcss injects toggle variable initialization wherever it sees color-scheme. But when light-dark() and color-scheme are in separate files (as with XDS, where tokens are in xds.css but color-scheme is set by XDSTheme via StyleX), the polyfill vars are used but never defined, breaking all colors. Fix: add `color-scheme: light dark` to: - reset.css — on :where(html), the canonical place for the declaration. Every XDS app imports this first. - build-css.mjs output (xds.css) — for consumers who import xds.css without reset.css - build-theme.mjs output (theme.css) — for theme files containing light-dark() values This makes XDS CSS compatible with any bundler that runs lightningcss regardless of target configuration. Reverts the cssMinify: false workarounds from PR #623 and earlier (PRs #558, #566). Co-authored-by: Navi <navi@navibot.dev>
cixzhang
added a commit
that referenced
this pull request
Mar 15, 2026
LightningCSS lowers light-dark() into --lightningcss-light/--lightningcss-dark polyfill variables for older browsers. This polyfill actually works correctly IF the color-scheme declaration is in the same CSS file — lightningcss injects toggle variable initialization wherever it sees color-scheme. But when light-dark() and color-scheme are in separate files (as with XDS, where tokens are in xds.css but color-scheme is set by XDSTheme via StyleX), the polyfill vars are used but never defined, breaking all colors. Fix: add `color-scheme: light dark` to: - reset.css — on :where(html), the canonical place for the declaration. Every XDS app imports this first. - build-css.mjs output (xds.css) — for consumers who import xds.css without reset.css - build-theme.mjs output (theme.css) — for theme files containing light-dark() values This makes XDS CSS compatible with any bundler that runs lightningcss regardless of target configuration. Reverts the cssMinify: false workarounds from PR #623 and earlier (PRs #558, #566). Co-authored-by: Navi <navi@navibot.dev>
cixzhang
added a commit
that referenced
this pull request
Apr 26, 2026
… breakage (#623) LightningCSS lowers CSS light-dark() into polyfill variables (--lightningcss-light/--lightningcss-dark) that are never initialized, silently breaking all XDS theming colors. This has bitten us 3 separate times (PRs #558, #566, #499) across different Vite configs. Changes: - apps/example-vite/vite.config.ts: add build.cssMinify: false - apps/storybook/vite.config.ts: add build.cssMinify: false - apps/example-vite/README.md: add lightningcss gotcha as top entry, detailed explanation section, and update inline config example - apps/example-nextjs/README.md: add awareness note (Next.js uses PostCSS so not directly affected, but warn about custom minifiers) Co-authored-by: Navi <navi@users.noreply.github.com>
cixzhang
added a commit
that referenced
this pull request
Jun 21, 2026
… breakage (#623) LightningCSS lowers CSS light-dark() into polyfill variables (--lightningcss-light/--lightningcss-dark) that are never initialized, silently breaking all XDS theming colors. This has bitten us 3 separate times (PRs #558, #566, #499) across different Vite configs. Changes: - apps/example-vite/vite.config.ts: add build.cssMinify: false - apps/storybook/vite.config.ts: add build.cssMinify: false - apps/example-vite/README.md: add lightningcss gotcha as top entry, detailed explanation section, and update inline config example - apps/example-nextjs/README.md: add awareness note (Next.js uses PostCSS so not directly affected, but warn about custom minifiers) Co-authored-by: Navi <navi@users.noreply.github.com>
cixzhang
added a commit
that referenced
this pull request
Jun 21, 2026
… breakage (#623) LightningCSS lowers CSS light-dark() into polyfill variables (--lightningcss-light/--lightningcss-dark) that are never initialized, silently breaking all XDS theming colors. This has bitten us 3 separate times (PRs #558, #566, #499) across different Vite configs. Changes: - apps/example-vite/vite.config.ts: add build.cssMinify: false - apps/storybook/vite.config.ts: add build.cssMinify: false - apps/example-vite/README.md: add lightningcss gotcha as top entry, detailed explanation section, and update inline config example - apps/example-nextjs/README.md: add awareness note (Next.js uses PostCSS so not directly affected, but warn about custom minifiers)
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Problem
Vite's default CSS minifier (LightningCSS) "lowers" the native CSS
light-dark()function into--lightningcss-light/--lightningcss-darkpolyfill variables. These polyfill variables are never initialized, so every XDS color token silently becomes empty — all theming breaks with no visible error.This has bitten us 3 separate times across different Vite configs:
The root cause: setting
lightningcssTargetson the StyleX plugin is not sufficient. Vite's build-phase CSS minifier runs independently from the StyleX plugin and still mangleslight-dark()values in any CSS it processes (including pre-compiled dist CSS).Fix
Add
build: { cssMinify: false }to every Vite config that builds XDS packages. This is safe because XDS dist CSS is already minified.Config changes
apps/example-vite/vite.config.ts— addcssMinify: falseapps/storybook/vite.config.ts— addcssMinify: falseDocumentation changes
apps/example-vite/README.md— add LightningCSS as the Adding Code of Conduct file #1 gotcha entry, detailed explanation section, and update the inline Vite config example to includecssMinify: falseapps/example-nextjs/README.md— add awareness note (Next.js uses PostCSS so not directly affected, but warn about custom CSS minifiers)The internal vibe-test configs (
vite.config.ts,vite.config.preview.ts,vite.config.report.ts) already havecssMinify: falsefrom the earlier fixes.