cssnano Files

What's Changed

New Features

• Merge corner border-*-radius longhands into border-radius shorthands. Four complete corner declarations in the same importance lane now collapse into one shorthand, with horizontal and vertical axes minified independently and separated by a slash when distinct.

Bug fixes and Improvements

• Merge margin, padding, border, border-radius, columns, and border-spacing declarations inside at-rule containers such as @page, @position-try, and nested at-rules. Fold identical horizontal and vertical border-spacing components to a single value. Recognize columns shorthands combining a count and a math function in either order, and preserve invalid declarations as written: border shorthands with multiple styles and columns values combining CSS-wide keywords with widths or counts no longer discard preceding valid longhands.

• Preserve percentage units in registered custom-property initial values with composite syntax, ranges, groups, and multipliers, and avoid clamping numeric operands nested inside alpha-value functions.

• Restrict color minification to CSS properties that accept <color> and custom properties, preserving custom identifiers in properties like animation-name, grid-area, and counter-reset. Add support for hwb() color values and minification inside color-mix(), light-dark(), and var() fallbacks, while preserving relative color syntax, math functions, and token boundary separators.

• Preserve zero percentage units in rgb(), rgba(), and modern CSS Color 4 functions to avoid invalid syntax, respect disabled time conversions for 0ms, clamps percentage opacity values adhering to CSS Color 4 alpha semantics, and improve compatibility with uppercase at-rules and vendor-prefixed keyframes.

• Preserves zero length in columns shorthands and zero units inside @property with <angle-percentage> syntax, retaining keyframe percentage units under nested rules. Symmetrically rounds negative numbers when precision is configured, converts between metric units (mm, cm, q), preserves zero percentages on SVG stroke properties to retain transition interpolation, and caches Browserslist lookups across runs. Also preserves units inside CSS Fonts 5 override descriptors, anchor() functions, flex-basis, and IE-targeted sizing properties.

• Remove comments more reliably and preserve the ones you keep exactly. Comments are now removed from !important declaration values and comment detection respect CSS token boundaries: text inside unquoted url() values and behind escape sequences in strings and identifiers is no longer mistaken for a comment. Kept comments are emitted byte-for-byte, including an unclosed comment at the end of a value, and whitespace inside kept comments is left untouched. Removal state is scoped to each document, so a shared processor no longer carries removeAllButFirst first-comment state between runs, and the remove callback runs once per comment occurrence. A non-function remove option now fails with a TypeError.

• Improve conformance for modern CSS math functions, grid-line values, and case-sensitive attribute selector modifiers while preserving ambiguous or invalid declarations. The affected transforms now use bounded, linear scans for these forms.

• Value transforms now read the CSS Values 4 math function names from one mathFunctions table in cssnano-utils, so unit retention, box and shorthand merging, parameter and whitespace handling, and time classification agree on which functions count as math functions. Serialized output is unchanged.

• Standardize output normalization for margin, padding, and physical border properties. Property names and case-insensitive keywords in generated shorthands and normalized standalone shorthand declarations are canonicalized to lowercase, while preserving author casing for unmerged longhands, custom properties, hack prefixes, and unresolved values.

• perf: median 15% speed increase on test fixtures

• postcss-normalize-url now decodes quoted url(...) values, preserving literal backslashes and escape sequences whether quotes are stripped or kept. Relative URLs now normalize using POSIX path semantics across all platforms, and converted @namespace URLs escape double quotes.

• Join every escaped line continuation in a multiline url() value into one line, including \r\n continuations that previously left an invalid string behind. Rewriting a @namespace URL no longer overwrites the tokens that follow it, so trailing text is preserved and multiple URLs in one namespace declaration are each normalized.

• Remove insignificant whitespace around custom-property names and, in standard declarations, around env() custom-ident arguments and around comma delimiters in var(), env(), and constant(). Between a custom-property name and its value, only the parser-consumed leading whitespace run is dropped; authored whitespace elsewhere in the value, such as after a preserved comment, is preserved per CSS Variables 2. Required whitespace between distinct tokens and the single whitespace token in an empty fallback remain preserved, and a preserved comment kept between a declaration name and value now survives minification, for custom properties and standard declarations alike. Comment removal in selectors and values no longer fuses the tokens the comment in-between: an attribute case-insensitivity flag or any other name-like token keeps its boundary, and math-operator spacing is restored for every function whose value productions accept <calc-sum> arguments (including calc-size(), calc-mix(), and random()). Values without comments are now left byte-for-byte untouched rather than re-spaced.

• Preserve whitespace around division operators across all modern CSS math functions such as min(), max(), and clamp(), and trim extraneous whitespace from commas in nested calculations.

• Order columns: 2 auto as columns: auto 2. Leave animation declarations with negative iteration counts unchanged. Reorders border and box-shadow math functions that resolve to a length, such as calc(1px + 1em), and leaves other math unchanged. Passes through unknown box-shadow color functions instead of reordering them.

• Merge duplicate @keyframes and @counter-style definitions more conservatively.

• Use ASCII case-insensitive matching for CSS names and grammar keywords so Unicode lookalikes are preserved, and restrict CSS whitespace normalization to the CSS whitespace set.

• Rename identifiers only when their definition and a reference are in the same stylesheet; leave alone names inside var(), env(), attr(), or a custom property fallback; skip reserved words in the encoder; rename reversed() counters and implicit <area>-start/-end lines with their area.

• Preserve Windows drive roots, directory dot references, and leading ./ prefixes when the first relative segment contains a colon. Decode unreserved percent-encoded octets while preserving percent-encoded dots, normalize @import at-rules including nested condition URLs, retain quotes for URLs containing non-printable control characters, avoid unnecessary declaration tokenization, and synchronize raw parameters.

• Minify equal shorthand components for two-axis, four-side, alignment, aspect-ratio, and transition declarations while preserving grammar-sensitive and invalid values.

• fix(postcss-minify-params): support CSS values level 4 and Media Queries level 5

• Preserves invalid selector syntax and namespace-sensitive universal selectors while safely normalizing pseudo-element, View Transition, and keyframe forms. Recognizes the full token grammar for An+B formulas, including escaped forms and exact large integers.

• fix(postcss-ordered-values): improve performance and correctness

• Aligns SVG data URI processing with WHATWG URL standards by treating the first # as the fragment delimiter. Non-conforming data URLs (such as those with malformed percent-encoding or where an unencoded # in markup truncates the SVG payload) are left untouched rather than parsed with an internal XML recovery scanner. CSS hex escapes in the URI scheme (for example d\61ta:image/svg+xml) reach the optimizer. SVG data URIs inside CSS Values 4 src(...) functions or url(...) declarations with url-modifiers are optimized while preserving modifiers and comments. Minified declarations also keep their raw value metadata in sync.

• Unify physical-border optimization under a single reducer that chooses deterministic shortest non-crossing canonical shorthands from complete side and component groups, partitioned by importance lane. Partial grids no longer require a full border reset. Dynamic declarations, style hacks, CSS-wide keywords, support fallbacks, unresolved substitutions, and other cascade barriers remain in their original positions, while valid fallback and border-image behavior is preserved.

• Parse font weights and column units from tokenizer metadata. This safely minifies escaped bold weights, recognizes escaped length units, and prevents partial rewrites of invalid font shorthands while preserving original source spelling.

• Update browserslist

• Preserve matching-importance all reset boundaries when merging margin, padding, physical border-radius, and columns declarations, so minification does not restore values cleared by the reset.

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.0.5...cssnano@9.1.0