What's Changed

• fix(postcss-discard-duplicates): remove redundant sibling at-rules in #2010

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.2.0...cssnano@9.2.1

Features

• Merge box alignment properties into the place-content, place-items and place-self shorthands, such as align-items:center;justify-items:start into place-items:center start. This only happens when every browser in your Browserslist targets supports the shorthands, because a browser that does not would ignore both alignments. The defaults query includes browsers with unknown support, such as Opera Mini and UC Browser, so it keeps the longhands. Values that use safe, unsafe or last baseline merge only when both values use the same keywords. postcss-merge-longhand now accepts the Browserslist options overrideBrowserslist, stats, path and env.

Fixes

• Write numbers in scientific notation when it is shorter, such as 1e-6px for 0.000001px and 1e6px for 1000000px. This also applies when length unit conversion is disabled. Numbers written without a decimal point, such as z-index:1000000, keep their form, because an <integer> cannot use scientific notation.

• Stop merging longhands across a nested rule or at-rule. The shorthand ended up after the nested rule and overrode it, so in a{margin-top:1px;&{margin-top:2px}…} the nested margin-top was lost. This applies to margin, padding, border, border-radius and columns. Declarations on each side of a nested rule are now merged separately. An at-rule without a block, such as @apply x;, also separates them, since it may add declarations. An empty rule such as &{} does not. A border-image or all declaration before a nested rule no longer prevents merging the border longhands after it.

• Stop merging rules that have an invalid selector, such as b: hover, [a b], :lang(en fr) or a||b. An invalid selector makes the whole selector list invalid, so the browser also dropped the valid rule it was merged with.

• Only treat a dimension as the font size in the font shorthand when it has a length unit. An invalid value such as font:bold 1s "Arial Black" is now left unchanged.

• Leave the font shorthand unchanged when it contains attr(), if(), inherit() or a custom function such as --name(), as already done for var() and env(). Their result is only known when the browser computes the value.

• Remove a zero color stop position only when it has the right type for the gradient. conic-gradient() now drops 0deg and keeps an invalid 0px, while linear and radial gradients still drop 0px. -webkit-linear-gradient() keeps to bottom and other to directions as written, since the prefixed syntax measures angles differently.

• Stop turning a comment inside a selector into a descendant combinator. A comment is not whitespace, so .a/**/.b selects elements with both classes, including inside :is(), and is no longer rewritten as .a .b. Invalid selectors such as div/**/span are left as written instead of becoming valid.

• Leave rules with an invalid selector unchanged, including an ID selector that starts with a digit, such as #1a, and a combinator after a pseudo-element, such as a::before b.

• Shorten top center and bottom center to top and bottom, instead of 0 and 100%, which the browser reads as horizontal positions. center top and center bottom are now shortened the same way.

  Leave a position unchanged when it cannot be safely rewritten:

  • in a background layer where another value splits the position, as in left no-repeat center, which is invalid;
  • when it contains a function such as attr(), if() or a custom --function(), which may return a keyword, as var() already did;
  • when an invalid three-value position contains a math function, such as left abs(1px) top, as calc() already did.

• Keep strings unchanged when removing a line continuation (a backslash before a newline) right after an escape. In "\31 followed by a line continuation and 2", joining the lines would turn \31 into \312, so the result is now "\31 2".

  Leave @charset unchanged. Browsers only recognize it with double quotes, so rewriting single quotes would make an ignored @charset take effect.

• Update postcss-calc to 11.2.2. postcss-calc() now attempts to preserve fractions if the replacement would lose too much precision

What's Changed

• fix: collapse redundant whitespace in at-rules in #1999

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.1.1...cssnano@9.1.2

What's Changed

Bug Fixes

• fix(postcss-convert-values): preserve unicode range in #1995

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.1.0...cssnano@9.1.1

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

What's Changed

Bug Fixes

• fix(postcss-svgo): decode SVG following WHATWG specification in #1975

Other changes

• Update dependencies

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.0.4...cssnano@9.0.5

What's Changed

• fix: update postcss-calc in #1970

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.0.3...cssnano@9.0.4

What's Changed

• fix: update color parsing library in #1964

• fix: update PostCSS and selector parser

• fix: update conflict detection and color conversion CSS spec conformance

• fix: update PostCSS peer dependency

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.0.2...cssnano@9.0.3

What's Changed

• fix: add main and types to package manifests in #1958
• fix: update postcss-calc

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.0.1...cssnano@9.0.2

What's Changed

• refactor: some small performance gains in #1955

Full Changelog: https://github.com/cssnano/cssnano/compare/cssnano@9.0.0...cssnano@9.0.1