perf: rework PostCSS pipeline (purge-first order, cssnano default, browserslist)#2051
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- Reorder plugins to purgecss -> autoprefixer -> cssnano so prefixing and
minification only run on rules that survive the purge.
- Drop the cssnano `advanced` preset (and the cssnano-preset-advanced dep) for
the `default` preset: advanced was measured to add < 0.2% over default, while
dropping cssnano entirely costs ~5-8%, so default is kept.
- Pin Bootstrap 5.3.8's browserslist in package.json so autoprefixer targets the
browsers Bootstrap itself supports instead of autoprefixer's implicit defaults.
- De-duplicate config: exampleSite/config/postcss.config.js now re-exports the
theme root config. Hugo restricts the PostCSS Node process to the site dir, so
the exampleSite widens security.node.permissions.allowread to '../config'.
- Trim the safelist: drop the d-{bp}-table-cell regex (render-table.html emits
the configured breakpoint class into the markup, so it reaches hugo_stats.json
and survives purge on its own now that purge runs against complete stats), and
document why every remaining entry is JS-injected and cannot be seen in stats.
exampleSite purge-ON build: green, deterministic (run-vs-run 0-diff), selector
audit 0 over-purges, 257,473 B (46,539 gzip, slightly under stock).
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markdumay
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July 17, 2026 17:01
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What
Reworks the PostCSS config so purge runs first and the pipeline ships fewer bytes with fewer
dependencies:
purgecss → autoprefixer → cssnano(wasautoprefixer → cssnano → purgecss). Prefixing and minification now only touch rules that survive the purge.advanced→defaultpreset and drop thecssnano-preset-advanceddependency.Measured on the exampleSite:
advancedadds < 0.2% overdefault, while dropping cssnanoentirely costs ~5–8% — so cssnano stays on the default preset.
package.jsonso autoprefixer targets Bootstrap'sown supported browsers rather than autoprefixer's implicit
defaults.exampleSite/config/postcss.config.jsnow re-exports the theme rootconfig. Hugo restricts the PostCSS Node process to the site dir
(
security.node.permissions.allowread), so the exampleSite widensallowreadto'../config'./^d-(sm|md|lg|xl|xxl)-table-cell$/regex —render-table.htmlemits the configured-breakpoint class into the markup, so it reaches
hugo_stats.jsonandsurvives purge on its own now that purge runs against complete stats. Every remaining safelist
entry gets a one-line reason (all are JS-injected classes PurgeCSS cannot see in stats).
Evidence (exampleSite, purge-ON,
hugo --gc --minify)main.css257,473 B / 46,539 B gzip — slightly under the prior advanced-presetbuild (257,673 / 46,612).
-webkit-, 23-moz-.hugo_stats.jsonthat has a rule in the unpurged CSSsurvives purge — 0 genuine over-purges (an ancestor-aware audit; the only naive flags were
.hero-image-full-height .hero-*compound rules whose ancestor class is unused, correctly purged).Part of the styles-pipeline modernization program (slice S3). Held pending the maintainer
merge gate. Note: S2 (guarded
style.purgedefault flip) will follow and its QA runs against this config.