[Jarred-Sumner]

What does this PR do?

Consolidates the open pull requests on the CSS parser (src/css: parsing, minifying, lowering, printing, CSS modules) into one.

179 open pull requests were in scope. Each was judged by one rule: the output must mean to a browser what the input meant. Every claim was run through a build of main, a build with the change, lightningcss 1.33 and Chromium 156 (CSSOM, computed values, painted pixels for colors and gradients), and counted against 10,116 real stylesheets: the published CSS of about 190 popular npm packages, plus stylesheets from open source repositories. 107 land here, whole or in part, most of them cut down. The source diff is net negative.

Of the 10,116, 9,509 are stylesheets that someone ships. The rest are test fixtures of other tools (521), Tailwind v4 source that needs its plugin (59) and SCSS, PostCSS or template source (27).

9,509 shipped stylesheets	main	this branch
fail to build	71	35
... of those, valid CSS that Bun rejects		0
minified output reads differently in Chromium than the input	552	2
CSS modules with a name that is referenced but not defined, or exported but not defined	166	0

all 10,116	main	this branch
fail to build	192	141
minified output reads differently in Chromium than the input	593	15
build on main, fail here		0
right on main, wrong here (minified, and at the default targets)		0
size of the minified output, no targets	162.32 MB	162.47 MB (+0.093%)
size of the output at the default targets	224.1 MB	210.2 MB (-6.2%)

A syntax error is a build error, with one exception: the IE star hack *zoom: 1 is skipped, because tachyons and handsontable ship it. The 35 shipped stylesheets that fail are invalid CSS: 28 have a selector that Chromium drops (semantic-ui-css, swiper, @ionic/core, Adobe Spectrum, xp.css), 2 an @import after other rules, and one each @supports not X and Y, a nested @keyframes, a stray comma, a selector list in ::slotted(), @media screen\0 (govuk-frontend). The 2 that read differently fold a color-mix() inside a gradient (see the known gaps).

The growth of the minified output is rules and declarations that main deleted by mistake: 87 KB of rules, 45 KB of prefixed declarations that only browser targets can rule out.

Popular CSS that main breaks today

• normalize.css, modern-normalize, sanitize.css: font-family: monospace, monospace is collapsed to monospace, which changes the font size from 16px to 13px (css: keep repeated font families and dedupe only the inserted system-ui fallbacks #46662).
• CKEditor 5, Tabler, Carbon, VitePress, Ionic, PatternFly, Excalidraw: a rule of custom properties is deleted as a "duplicate" of a later rule with the same selector and other custom properties. 37 stylesheets lose 1,681 custom properties (css: compare custom property names in PropertyId equality and importance in duplicate-rule detection #33684).
• Material Components, daisyUI, DocSearch, plyr: a var() size loses to its own fallback (css: keep an unparsed width/height/color after the declarations written before it #42101).
• nextra, daisyUI, CKEditor: declarations written after a nested rule are moved above it (css: keep declarations written after a nested rule in place with a nested declarations rule #45462).
• antd 4, purecss, govuk-frontend: browser hacks in selector lists start to apply everywhere (css: keep a selector list whole when a member is vendor prefixed #42100).
• foundation-sites, flatpickr, 98.css, blueprintjs, scalar, react-datepicker: the build fails on valid CSS (css: keep <general-enclosed> media and container conditions as written #46756, css: keep scanning an @supports condition after a nested block #38552, css: only reject bare :global / :local pseudo-classes in CSS modules #38534). tachyons, handsontable: it fails on the IE star hack (css: parse the *property hack as a declaration #46751).
• nodejs.org, Mantine: a CSS module exports classes that no rule defines, because the @apply or @mixin in them is moved out of the rule (css: keep unknown at-rules inside their style rule when nesting is compiled away #46759).
• hint.css and 42 more: z-index: 1000001 and 1000000 become the same number (css: print integers below 2^24 in full and long integer tokens as written #46715).
• Adobe Spectrum: --version: 5.0.1 prints as 5.1.
• A quarter of all stylesheets: minified output has a stray space in align-items: center (css: print align-items:center without a stray space when no safe/unsafe keyword is given #41993).

Behavior changes to look at first

1. light-dark() is kept as written at the default browser targets (css: keep light-dark() as written under the default browser targets #42009). The lowered form var(--buncss-light, a) var(--buncss-dark, b) is invalid unless a compiled color-scheme covers the element: 184 of the 215 real stylesheets that get it never define the variable, so every browser drops the declaration. The docs section on the polyfill is removed.
2. border is not built from longhands (css: only synthesize border / transition when the rule sets every longhand they reset #42072): border-width:0;border-style:solid;border-color:red stays three declarations, because border also resets border-image. 305 real stylesheets grow by 30 KB in total; bootstrap.min.css by 113 bytes, 5 gzipped. No real stylesheet was found where the old merge shows, so this is the one to drop if size matters more. 14 existing expectations change.
3. A CSS module no longer exports names that only occur inside :global(...) (css modules: decide local vs global at parse, fixing :global() exports and & inside :global() #45487). 73 real modules lose 202 export keys, all of them names that no rule has. import { g } or composes: g of such a name becomes a build error.
4. Container names and @counter-style names stay global in a CSS module (fix(css): keep container names global in CSS modules #45247 by @mikamikasuki). main hashes the @container name but not container-name, so a named query never matches. postcss-modules (Vite, css-loader, Next.js) keeps them global; lightningcss and esbuild hash both. Global keeps a container that is queried from another file or from JS working.
5. Syntax errors are build errors, also two that main lets through: a media query that stops short (@media screen and {, @media not {, @import "a.css" screen and;) and @media (width <) foo {. No stylesheet of the 10,116 has either. A condition that is valid by the grammar though no browser knows it, ( ... ) or fn( ... ), is kept as written (css: keep <general-enclosed> media and container conditions as written #46756): (min-width:0\0), (not(hover)).
6. Declarations after a nested rule stay where they were written, as a nested declarations rule (css: keep declarations written after a nested rule in place with a nested declarations rule #45462). Changes the output of 199 real stylesheets; in a fuzz of 2,850 nested programs compared by computed style, main was wrong in 1,056 and the pull request's code, before it was trimmed here, in none.
7. Bun.color: color() inputs are converted instead of returned as a string (Bun.color("color(srgb 1 0 0)", "hex") was "color(srgb 1 0 0)"); currentColor, system colors and light-dark() give null in the converting formats instead of the keyword as a string; a relative color or color-mix() outside sRGB is clipped, not gamut-mapped (hsl(from oklch(100% .399 336.3) h s l) is #ff5bff, was #fff).
8. The :-moz-any() and :-webkit-any() copies of rules with :is() are gone at the default targets (css: stop printing the :-moz-any() copy for Firefox 78, and regenerate the vendor prefix table from one caniuse-lite copy #45945, css: stop emitting :-webkit-any() copies of :is() that outrank the original rule #42029). The :-webkit-any() copy outranked the original rule: .title{color:blue} :is(h1,h2,h3){color:red} painted red. 5.8% of all default-target output was the :-moz-any() copies.
9. Property grows from 216 to 224 bytes: Url stores its text as a slice so that two url() values can be compared (css: compare url() values by their text #46895). The pull request packed a pointer and a u32 behind unsafe to avoid that.

Not in this PR, needs a decision

• Raise the default browser targets (css: bump the default browser targets to Vite's baseline widely available set #40369) and add a cssTarget option (Bun.build: add cssTarget option to set CSS browser targets #40368). Today: Chrome 80, Edge 80, Firefox 78, Safari 14, Opera 67, and no public way to change them. At Vite 8's floor the output of the 9,924 stylesheets is 15.3% smaller (3.9% gzipped). About a dozen fixes here only matter at today's floor, and code for older targets is unreachable without the option.
• Vendor prefixes for user-select, appearance, hyphens and five more (css: write the vendor prefixes for user-select, appearance, hyphens and five more properties #45814): 1,116 real stylesheets lack a prefix they need at the default targets. And for backdrop-filter (css: parse filter and backdrop-filter, and lower colors inside drop-shadow() #44648): 173.
• Clip instead of gamut-map in the sRGB fallback of a plain wide-gamut color: deletes about 90 lines, changes every pinned fallback hex. If the mapping stays, css: keep searching for the most saturated chroma under the JND in gamut mapping #44647 by @oddharsh makes it closer to what browsers paint (colors off by 2/255 or more: 168 to 110 of 3,170 real ones).

Changes

Rules: duplicates, merging, nesting, fallbacks

• The :-moz-any() copy of every rule with :is() or :not(a, b) is gone: Firefox 78 has :is() (css: stop printing the :-moz-any() copy for Firefox 78, and regenerate the vendor prefix table from one caniuse-lite copy #45945). 1,164 real stylesheets
• Keep declarations written after a nested rule in place with a nested declarations rule (css: keep declarations written after a nested rule in place with a nested declarations rule #45462). 379 real stylesheets
• With nesting compiled away, an unknown at-rule inside a style rule was moved out of it: .wrapper{@apply flex} printed a bare @apply flex; and the rule was gone, so a CSS module exported a class that no rule defines. It now stays in a block under the compiled selector. 72 real modules with Tailwind's @apply, 25 with Mantine's @mixin (css: keep unknown at-rules inside their style rule when nesting is compiled away #46759). 316 real stylesheets
• Keep !important in the rules generated for logical properties and color-scheme (css: keep !important in the rules generated for logical properties and color-scheme #38597). 311 real stylesheets
• With browser targets, remove an earlier duplicate rule only when its declaration block is equal (css: with browser targets, remove an earlier duplicate rule only when its declaration block is equal #46861). 171 real stylesheets
• Compare custom property names in PropertyId equality and importance in duplicate-rule detection (css: compare custom property names in PropertyId equality and importance in duplicate-rule detection #33684). 40 real stylesheets
• Keep same-condition @supports rules and empty named @layer blocks (css: keep same-condition @supports rules and empty named @layer blocks #46733). 31 real stylesheets
• Keep target-added vendor prefix passes on cloned and re-minified rules, and never print a bare :full-screen (css: keep target-added vendor prefix passes on cloned and re-minified rules, and never print a bare :full-screen #43339). 12 real stylesheets
• Keep the selectors on rules added for color fallbacks and logical properties (css: keep the selectors on rules added for color fallbacks and logical properties #43240). 3 real stylesheets
• A later declaration of a property drops the @supports color copies of the earlier one, which printed after the rule and won (css: drop @supports color fallbacks that a later declaration of the same property replaces #45560). 2 real stylesheets
• Do not merge style rules in a stylesheet that holds revert-rule (css: do not merge style rules in a stylesheet that holds revert-rule #46953). 1 real stylesheets
• @import ... supports(-webkit-mask: none) kept its prefix (css: parse (property: value) @supports conditions as declarations and merge same-condition rules #38589)

Properties and shorthands

• Print align-items:center without a stray space when no safe/unsafe keyword is given (css: print align-items:center without a stray space when no safe/unsafe keyword is given #41993). 3,317 real stylesheets
• Emit the physical longhands instead of the inset shorthand for targets without it (css: emit the physical longhands instead of the inset shorthand for targets without it #38583). 1,452 real stylesheets
• Keep the stops of an upward gradient as written, and drop a 50% hint only at the midpoint (css: keep the stops of an upward gradient as written, and drop a 50% hint only at the midpoint #46790). 104 real stylesheets
• Emit unparsed border-block-* declarations when compiling logical borders (css: emit unparsed border-block-* declarations when compiling logical borders #38582). 89 real stylesheets
• Keep repeated font families and dedupe only the inserted system-ui fallbacks (css: keep repeated font families and dedupe only the inserted system-ui fallbacks #46662). 88 real stylesheets
• A width / height / min-* / max-* with var() or env() was printed before the plain fallback written above it, so the fallback won (css: keep an unparsed width/height/color after the declarations written before it #42101). 26 real stylesheets
• Keep box-orient and box-direction when flex-direction or flex-flow follows (css: keep box-orient and box-direction when flex-direction or flex-flow follows #45672). 16 real stylesheets
• Write held prefixed background declarations at every flush (css: write held prefixed background declarations at every flush #46882). 6 real stylesheets
• Derive equality for Size2D and BorderRadius, and keep every prefix in the border-radius handler (css: derive equality for Size2D and BorderRadius, and keep every prefix in the border-radius handler #45665). 2 real stylesheets
• Print none instead of an empty border-image, mask-border or mask-box-image value (css: print none instead of an empty border-image, mask-border or mask-box-image value #45143). 2 real stylesheets
• Keep font/transition sub-properties on the side of the shorthand they were written on (css: keep font/transition sub-properties on the side of the shorthand they were written on #41990). 2 real stylesheets
• CSS-wide keywords are not names: font:12px Arial;font-family:inherit printed font:12px inherit, color-scheme:inherit and color-scheme:auto printed normal, transition-property:unset was folded into transition (css: keep css-wide keywords and percentage stretch out of the font and transition shorthands #42022). 2 real stylesheets
• Only fold font longhands into font when the rule declared a font (css: only fold font longhands into font when the rule declared a font #45459)
• Keep a font family name quoted when its identifiers do not read back as the same name (css: keep a font family name quoted when its identifiers do not read back as the same name #46606)
• Stop rewriting valid positions into ones browsers reject (css: stop rewriting valid positions into ones browsers reject #45197)
• border is no longer built from longhands unless the rule also sets what border resets (border-image), and an author's border-image reset is no longer dropped. transition is likewise only written where the rule wrote one, because it resets transition-behavior (css: only synthesize border / transition when the rule sets every longhand they reset #42072)
• border; border-image: <gradient>; border-image-slice: 1 lost the gradient in every default build (css: keep border-image and border in source cascade order within a rule #42018)
• A prefixed linear-gradient keeps its direction, written or generated: the prefixed syntax names the starting side and measures angles differently (css: read a prefixed linear-gradient direction in the 2011 syntax #46697)

At-rules

• Print @font-face format() keywords as strings (Print @font-face format() keywords as strings #37979). 439 real stylesheets
• Print @supports not conditions without a leading space (css: print @supports not conditions without a leading space #38559). 88 real stylesheets
• Reset after the number token of a unicode-range (css: reset after the number token of a unicode-range #45835). 33 real stylesheets
• Keep <general-enclosed> media and container conditions as written (css: keep <general-enclosed> media and container conditions as written #46756). 24 real stylesheets
• A strict range such as (width < 768px) lowered for old targets still matched at exactly 768px. The step is now .02px. The not all and form for other units is not taken (css: lower strict media range bounds with not all and or a .02px step #46806). 18 real stylesheets
• Keep scanning an @supports condition after a nested block (css: keep scanning an @supports condition after a nested block #38552). 9 real stylesheets
• Every @counter-style name printed as @counter-stylename, which browsers drop (also css: print the space after @counter-style, and hash the counter style name in list-style in CSS modules #46692). In a CSS module the name now stays global, like the list-style that refers to it (css: fix @counter-style and @scope printer round-trip #33679). 9 real stylesheets
• Keep a keyframe whose block has an invalid item (css: keep a keyframe whose block has an invalid item #46288). 2 real stylesheets
• Read an @Property initial-value on the stylesheet's parser, keep an unmatched value as written (css: read an @property initial-value on the stylesheet's parser, keep an unmatched value as written #45806). 2 real stylesheets
• @media {} is all. A media query that stops after and, or or not (@media screen and {) is a build error; main printed not all or dropped the condition, silently. The @layer and type selector parts are not taken (css: make a media query, @layer name list or type selector that stops short a parse error #46869). 2 real stylesheets
• Accept a name-only @container and a style() feature with no value (css: accept a name-only @container and a style() feature with no value #46689). 1 real stylesheets
• Parse <timeline-range-name> <percentage> keyframe selectors (css: parse <timeline-range-name> <percentage> keyframe selectors #45652)
• Allow or inside parentheses after a media type (css: allow or inside parentheses after a media type #45088)
• Print the = comparison in media and container queries as = (css: print the = comparison in media and container queries as = #45071)
• Parse the @font-palette-values font-family descriptor as a list of family names (css: parse the @font-palette-values font-family descriptor as a list of family names #45484)

Selectors

• Never wrap a selector list in :is() (css: never wrap a selector list in :is() #46787). 414 real stylesheets
• Stop emitting :-webkit-any() copies of :is() that outrank the original rule (css: stop emitting :-webkit-any() copies of :is() that outrank the original rule #42029). 373 real stylesheets
• With browser targets, a selector list with a vendor-prefixed member was split, which revives hacks that rely on other engines dropping the whole list: .s *::-ms-backdrop,.s{flex:auto} applied everywhere. Rewritten; the list is printed as written (css: keep a selector list whole when a member is vendor prefixed #42100). 42 real stylesheets
• Print the vendor prefix on downleveled :any-link, :read-only, :read-write, :placeholder-shown and :autofill (css: print the vendor prefix on downleveled :any-link, :read-only, :read-write, :placeholder-shown and :autofill #42131). 12 real stylesheets
• Fix nesting lowering of a & that does not lead its selector (css: fix nesting lowering of a & that does not lead its selector #43047). 8 real stylesheets
• @scope: & and implicit selectors compile to :where(:scope), relative selectors and bare declarations parse (css: fix @scope nesting, relative selectors, and declarations in @scope #43165). 7 real stylesheets
• Only reject bare :global / :local pseudo-classes in CSS modules (css: only reject bare :global / :local pseudo-classes in CSS modules #38534). 5 real stylesheets
• Stop truncating @scope to (...) and stop replacing & in the scope-end selector (css: stop truncating @scope to (...) and stop replacing & in the scope-end selector #43146). 2 real stylesheets
• [xl|href$=".pdf"] lost its namespace prefix (css: keep the namespace prefix on attribute selectors that have an operator #45159). 2 real stylesheets
• Match An+B keywords exactly and take only + as the leading sign (css: match An+B keywords exactly and take only + as the leading sign #42953). 1 real stylesheets
• Parse ::details-content and ::picker() like ::part() (css: parse ::details-content and ::picker() like ::part() #45504). 1 real stylesheets
• Parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection (css: parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection #45815)
• Print :nth-col(1) and :nth-last-col(1) in functional form (css: print :nth-col(1) and :nth-last-col(1) in functional form #41575)
• li::before::marker failed the build (css: accept ::marker directly after ::before and ::after #45810)
• & inside :nth-child(... of S) is resolved when nesting is compiled away. The second selector serializer (326 lines) is deleted (css: resolve & inside :nth-child(... of S), :host(), ::slotted() and ::cue() #43024)

Colors and Bun.color

• Keep light-dark() as written under the default browser targets (css: keep light-dark() as written under the default browser targets #42009). 227 real stylesheets
• Number and percentage channels parse in lab(), lch(), oklab(), oklch(), hsl() and hwb(); the hue of lch / oklch is no longer scaled by alpha (css: parse number and percentage channels in lab(), lch(), oklab(), oklch(), hsl() and hwb() #45084). 130 real stylesheets
• Bun.color returns null for currentColor, system colors and light-dark() in the converting formats, instead of the CSS keyword as a string (Bun.color: return null for unconvertible colors, fix hsl/lab output, lab() and named-color parsing #33047). 130 real stylesheets
• Relative colors: channel keywords are on the scale of their function (rgb(from #369 calc(r + 10) g b)), the origin's alpha is kept, a relative color kept as written gets no @supports copies, and a result outside sRGB is not folded (css: fold relative colors on the scale of their function, and keep them as written when the fold is not exact #45362). 31 real stylesheets
• Keep rotate: 0deg out of none, and keep the origin alpha in relative colors (css: keep rotate: 0deg out of none, and keep the origin alpha in relative colors #38486). 13 real stylesheets
• Compute the D50 reference white in f32 so greys convert to lab(l 0 0) like lightningcss (css: compute the D50 reference white in f32 so greys convert to lab(l 0 0) like lightningcss #38535). 7 real stylesheets
• Return a missing hue for a grey from conversions into lch, oklch, hsl and hwb (css: return a missing hue for a grey from conversions into lch, oklch, hsl and hwb #45201). 5 real stylesheets
• Fix color(a98-rgb), srgb-linear relative colors and color-mix(in xyz-d50) (css: fix color(a98-rgb), srgb-linear relative colors and color-mix(in xyz-d50) #38487). 4 real stylesheets
• Match named colors without regard to ASCII case (css: match named colors without regard to ASCII case #45092). 3 real stylesheets
• Fold min(), max() and clamp() over plain numbers (css: fold min(), max() and clamp() over plain numbers #39515)
• calc(l - .08) in a percentage channel of a relative color became NaN and printed #000 (also css: fail a percentage calc that cannot be reduced instead of folding it to NaN #45970) (css: read a NaN calculation in a color channel as 0, not none #45971)
• Bun.color: convert color() inputs instead of returning them as a CSS string (Bun.color: convert color() inputs instead of returning them as a CSS string #38488)
• A color-mix(in srgb, ...) result outside sRGB prints color(srgb ...) instead of a gamut-mapped hex (css: clip color-mix() results outside the sRGB gamut instead of gamut mapping them #39269)

calc() and numbers

• Rounding to 6 significant digits ate into the integer part: z-index:2147483647 became 2147480000, max-width:9999999px became 10000000px, --x:1234567.5 became 1234570. It now only cuts a fraction short: a value kept as tokens prints its source text, a typed value prints every integer digit and at least one digit of the fraction (css: print integers below 2^24 in full and long integer tokens as written #46715). 43 real stylesheets
• A number without a unit is no longer repaired into px (height:1.5715 is dropped by a standards-mode browser, so it prints as written), calc(-1 * 0) is not a length, and on a property of the range [0,∞] (sizes, border radii, padding, border and outline widths, gap, flex-basis, font-size) a calc() that folds below zero prints 0 instead of an invalid negative literal, and a negative literal no longer replaces the valid declaration before it (width:10px;width:-5px printed width:-5px) (css: treat out-of-range and unit-less numeric values as invalid instead of merging or repairing them #42104). 24 real stylesheets
• Print numbers from the f32's shortest digits, not its f64 expansion (css: print numbers from the f32's shortest digits, not its f64 expansion #38565). 17 real stylesheets
• Print negative numbers below 1 with a single minus sign (css: print negative numbers below 1 with a single minus sign #38516)
• Keep math functions over two different length units as written (css: keep math functions over two different length units as written #38489)
• Fold rem() with a truncated quotient, so it keeps the sign of the dividend (css: fold rem() with a truncated quotient, so it keeps the sign of the dividend #32286)
• A one-argument min() / max() around a sum printed without any function (width:100% - 20px) (css: wrap a one-argument min()/max() sum in calc() and give hypot() one fold for every argument count #46145)
• round() breaks ties upward and handles a negative step as browsers do (css: fold round() by choosing between the lower and upper multiple of |B| #45249)

CSS modules

• A CSS module exports its @keyframes names (styles.spin). Hashing is unchanged (css modules: make @keyframes and animation names symbols and export them #46720). 145 real stylesheets
• A name inside :global(...) prints plain but was exported as name_<hash>, a class no rule has (also css modules: keep names inside :global(...) out of the exports object #38573) (css modules: decide local vs global at parse, fixing :global() exports and & inside :global() #45487). 90 real stylesheets
• Keep container names global in CSS modules (fix(css): keep container names global in CSS modules #45247). 6 real stylesheets
• Tag the keyframes name when an animation value falls back to raw tokens (css modules: tag the keyframes name when an animation value falls back to raw tokens #46034). 6 real stylesheets
• In a plain stylesheet composes: a from "./b.css" was treated as an import: the file was inlined and an absolute path printed (css: parse composes as CSS modules syntax only in a CSS module #45961). 4 real stylesheets
• Drop a rejected composes instead of failing the file at print time (css modules: drop a rejected composes instead of failing the file at print time #38538). 1 real stylesheets
• Keep every rule's custom properties for the composes conflict check (css modules: keep every rule's custom properties for the composes conflict check #38523)
• Keep composes working after a nested rule in the same block (css modules: keep composes working after a nested rule in the same block #38520)
• IdentOrRef::hash read 2 of 16 bytes, so in release builds every class of a module hashed alike (css: hash full Ref identity in IdentOrRef::hash #30784)

Tokens, url(), diagnostics

• The block skip stack no longer allocates on every block exit (css: keep the block skip stack inline and off the cold path #39533)
• Report the diagnostic's line without its line breaks in position.lineText (css: report the diagnostic's line without its line breaks in position.lineText #38342). 192 real stylesheets
• Compare url() values by their text (css: compare url() values by their text #46895). 26 real stylesheets
• Values kept as tokens keep the blanks they were written with instead of having them re-invented at print time: attr(x type(<number>)) printed type(< number> ), which browsers drop. Minified output still drops the blanks that cannot matter (css: keep whitespace and comments in token lists #45577). 19 real stylesheets
• The IE star hack (*zoom:1) failed the whole build. The declaration is skipped, as every browser does. It is the one syntax error that builds: tachyons, handsontable and jasmine ship it (css: parse the *property hack as a declaration #46751). 8 real stylesheets
• The path of a copied asset spliced into url() is always quoted, so a file name with a space or a parenthesis cannot end the url() (css: quote and escape the asset path spliced into url() #41557). 7 real stylesheets
• Move the skip loop of parse_until_before out of the generic body (css: move the skip loop of parse_until_before out of the generic body #39520)
• Remove dead code from bun_css: the unused impl Default for Property (Remove dead code from bun_css: the unused impl Default for Property #45618)
• Default the at-rule and qualified-rule parser traits, drop the url_to_css shim (css: default the at-rule and qualified-rule parser traits, drop the url_to_css shim #31999)

Speed

Four inputs that took quadratic or exponential time, or produced output out of proportion, are now linear, with no new limit and no extra pass (#31639, #42243, #38531, #43421).

Tests only

• css-fuzz.test.ts never ran in CI and timed out on debug builds; it is a deterministic table now (test(css): replace the random css-fuzz loops with a deterministic table #38500)
• nth-anplusb-ident.test.ts counts heaps in a child process (test: count the heaps of the An+B selector test in a child process #46331)
• color.test.ts checks the ansi-16 sweep with one expect() (test: check the ansi-16 color sweep without an expect() per color #42824)
• Not CSS, but it failed this PR's CI and fails on main too: ws-proxy.test.ts on Windows, "a message sent during a TLS renegotiation arrives after it". The helper server now renegotiates from the callback of the frame's write (test(ws-proxy): renegotiate only after the "renegotiating" frame is written #46170)

No pull request covered these

• --v: 5.0.1 printed as 5.1, --w: 1.0.0 as 10, --x: 1+2 as 12, 2n+1 as 2n1: a number token that touches another keeps its source text.
• color-scheme: auto printed as normal, and color-scheme: dark light as light dark.
• A bare :global or :local in a CSS module sets the scope of the names after it, up to the end of the selector, as in css-loader. It was a build error.
• The scrollbar states (a:horizontal, ::-webkit-scrollbar{&:horizontal{}}) are valid in a plain compound, as in WebKit and Blink.
• Without browser targets, -webkit-box-align, -ms-flex-align and the like were dropped next to their standard form (flatpickr, foundation-sites, materialize-css: 28 stylesheets), and -webkit-fill-available before -moz-available (beercss).
• (-o-min-device-pixel-ratio: 2/1) printed as 2.
• sin(), cos() and tan() are exact at multiples of 90deg: calc(100px * cos(90deg)) printed -.00000437114px.
• A display-p3 color at targets that have P3 but not the other color() spaces (Safari 10.1 to 14) got itself as a fallback.
• width: rem(-18px, 5px) folds to a negative literal once rem() is right; it prints 0.
• Consecutive nested declarations rules, which arise when same-query @media blocks in one rule merge, are folded into one and count against the existing selector expansion limit as the &{} rules they replace did.

Known and not fixed here

• Four longhands are still folded into a transition the author did not write where the targets add a prefixed copy of a property (mask-image at Chrome 80): only the shorthand gives the copy its own times.
• A later background, box-shadow or border-* declaration still loses to the @supports copy of an earlier var() value of the same property with a wide-gamut color. Same on main; css: drop @supports color fallbacks that a later declaration of the same property replaces #45560 is taken for the properties of the fallback handler and for unparsed values only.
• A merged rule prints the unprefixed name in the passes of the rule it absorbed: .d::-webkit-input-placeholder{}.d::-moz-placeholder{} prints ::placeholder for the second (css: print explicitly prefixed selectors as written in every vendor prefix pass #42106, not taken: it breaks the merge of prefix-equivalent rules).
• The border, outline and font shorthands, line-height, scroll-padding, background-size and a few more still print a calc() that folds below zero as a negative literal. No real stylesheet has one.
• all is not a property Bun knows, so a{margin-top:1px;all:unset} prints all first. Same on main.
• A selector kept as raw tokens loses the blank before * when minified: --sel: .dark * prints .dark*. Same on main.
• width:calc(0% + 12px) folds to 12px, which lays out differently in a table cell. Same on main.
• The :dir() / :lang() rules of a lowered logical property print before the nested rules of their rule, so a logical declaration written after a nested rule of equal specificity still loses to it. Same on main.
• A fraction is still rounded to 6 significant digits (12345.678 prints 12345.7, 33.3333333333% prints 33.3333%). Keeping every digit would add up to 282 KB over the corpus.
• @keyframes "quoted" is hashed in a module but not exported.
• In a module, a keyframes name inside a var() fallback is not hashed: animation: var(--enter, fade 1s). Same on main.
• A color-mix() or relative color folded to a hex inside a gradient changes the interpolation from Oklab to sRGB (VS Code, clawhub). Printing color(srgb ..) instead needs a fallback for mask-image, list-style-image and custom properties at the default targets, which have none.
• A comma list in @container still fails the build.
• After a bare :global, names that are hashed at print time (::view-transition-old(foo)) are still hashed; inside :global(...) they are not.

Pull requests in scope that do not land here

• Duplicates of a pull request that lands here: fix(css): preserve quoted @font-face font-family and format() values #36961 (of Print @font-face format() keywords as strings #37979), css: dedupe font-family names in linear time #38478 (of css: keep repeated font families and dedupe only the inserted system-ui fallbacks #46662), css: keep empty named @layer blocks as @layer statements #38480 (of css: keep same-condition @supports rules and empty named @layer blocks #46733), css: print integer tokens from their i32 instead of a 6 digit float #38482 (of css: print integers below 2^24 in full and long integer tokens as written #46715), test(css): stop css-fuzz.test.ts from writing invalid.css into the cwd #38491 (of test(css): replace the random css-fuzz loops with a deterministic table #38500), css: interpolate color-mix() operands as css-color-4 specifies #38508 (of css: return a missing hue for a grey from conversions into lch, oklch, hsl and hwb #45201), css: parse calc(<channel> * <percentage>) in relative colors #38513 (of css: fold relative colors on the scale of their function, and keep them as written when the fold is not exact #45362), css modules: keep names inside :global(...) out of the exports object #38573 (of css modules: decide local vs global at parse, fixing :global() exports and & inside :global() #45487), test(css): build every css-fuzz generator input instead of mis-indexing the tables #38640 (of test(css): replace the random css-fuzz loops with a deterministic table #38500), css: scope container and container-name to the @container hash in CSS modules #45525 (of fix(css): keep container names global in CSS modules #45247), css: parse scroll-state() container queries #45589 (of css: keep <general-enclosed> media and container conditions as written #46756), css: fail a percentage calc that cannot be reduced instead of folding it to NaN #45970 (of css: read a NaN calculation in a color channel as 0, not none #45971)
• Already fixed on main: test(css): run the selector-list recovery cases through one child process #38674
• Right, but for input nobody writes (0 of 10,116 stylesheets, and not new syntax): css: budget selector expansion and nesting substitution by bytes #31916, css: print sub-1 dimensions without a fixed size scratch buffer #38526, css: compile the border-inline shorthands the border minifier produces for old targets #38592, css: convert color-mix() operands into hsl and hwb without gamut mapping them #39349, css: recognize :target-current, :target-before and :target-after #41139, css: decode ill-formed UTF-8 to U+FFFD before tokenizing #41801, css: make the all shorthand reset the declarations before it #42042, css: recognize :target-current, :target-before and :target-after #42484, css: use :is() for a nesting parent with a pseudo-element when more follows the & #43078, css: keep a url() in an at-rule prelude as written, and never print the resolved path of a url() #45604, css: keep an earlier transform or translate declaration when a target does not support the later one #45908, css: keep the legacy two-value -webkit-border-radius as its own declaration and print other -webkit- radii with three values #46086, css: fold hwb() above 100% to the gray W / (W + B) #46221, css: print a calc() product as a multiplication when the reciprocal of its factor is not finite #46224, css: read the font-family names of @font-palette-values without the generic-family table #46273, css: keep an earlier gap or flex-basis declaration when a target lacks the later one #46694, css: keep the slice and width of mask-border and -webkit-mask-box-image as written #46707, css: print :lang("") as a string #46737, css: decide the vendor prefixes of a background list per layer #46755, css: require at least one component in the background, transition, animation, mask, flex and flex-flow shorthands #46816, css: keep a prefixed gradient that uses the standard syntax as written #46870, css: keep the earlier copy of a file with a conditional layer in every import order #46934
• Right or harmless, but not worth their code, their bigger output or the behavior they change: css: migrate CssRule and DeclarationBlock to 'bump lifetime to eliminate unsound unsafe blocks #30905, css: bound light-dark() origin expansion depth in relative colors #31924, css: eliminate all unreachable!() via type-level hardening #33332, Move CSS hashing back to bun_css #34426, css: implement handle_composes to build CssModuleReference entries #36225, Bun.color: return null when input continues past the color #38006, css: emit the color-scheme fallback vars once when a block is minified again #38512, css: make the css_modules test option work and turn its bare test calls into real tests #38547, css: record the category when a margin, padding, inset or scroll-margin shorthand replaces the buffered values #38551, css: minify the scroll-padding properties #38561, css: warn about unknown bare pseudo-classes unless they are vendor prefixed #38572, css: drop the logical longhands a 4-side margin/padding shorthand overrides instead of flushing them #38576, css: drop the logical border longhands a border-width/style/color shorthand overrides instead of flushing them #38607, css: keep later physical declarations ahead of compiled logical ones #38623, css modules: report a composes property conflict at the declarations involved #38667, css: do not add transition entries the declaration already lists #38692, css: print explicitly prefixed selectors as written in every vendor prefix pass #42106, css: parse :active-view-transition-type() and the @view-transition rule #42912, css: parse :state(), ::highlight(), four css-pseudo-4 pseudo-elements, @position-try and @font-feature-values #42918, css: keep nested rules in source order across vendor prefix passes #43407, css: keep the vendor prefix passes of a rule in its @supports color fallbacks #43434, css: parse fill, stroke, caret-color and caret, and lower their colors #44700, css: store a calc() sum as one flat list of terms, and never drop or order a percentage of a length #45442, css: parse math functions in text-shadow lengths #45546, css: dispatch each declaration to the handler that owns its property #45747, css: compute asin, acos, atan, atan2, hypot, cbrt and log in Bun #45759, css: resolve legacy aliases in the name table and keep them after the property they alias #45825, css: write the -webkit-/-moz- device-pixel-ratio queries for resolution media features #45946, css: keep the prelude and block of an unknown at-rule as raw tokens #46061, css: read the float channels of an hsl(), hwb() or relative color origin #46127, css: parse transform-origin, perspective-origin and mask-position with their own grammars #46206
• Need a decision (see above), stay open: Bun.build: add cssTarget option to set CSS browser targets #40368, css: bump the default browser targets to Vite's baseline widely available set #40369, css: keep searching for the most saturated chroma under the JND in gamut mapping #44647, css: parse filter and backdrop-filter, and lower colors inside drop-shadow() #44648, css: write the vendor prefixes for user-select, appearance, hyphens and five more properties #45814
• Stays open: css: log parser warnings with the Source and a byte position #45787

Out of scope: CSS linking and chunking in the bundler, the dev server, docs-only pull requests, and repository-wide sweeps that touch src/css in passing.

Thanks to @mikamikasuki (#45247), @alii (#39520, #31999) and @oddharsh, whose measurements on #40369 and #41990 were used.

Fixes #16727.
Fixes #24770.
Fixes #30772.
Fixes #44704.
Fixes #45089.
Fixes #45237.
Fixes #46872.

How did you verify your code works?

• The 35 CSS test files pass on a debug build, also with FORCE_COLOR=1. 600+ of the tests in this branch fail on a build of main. An earlier head of this branch passed all 179 CI jobs that ran.
• The reproduction of each issue listed above was run on main (wrong) and on this branch (right).
• Differential run over the 10,116 stylesheets, main against this branch, minified without targets and through Bun.build at the default targets: no stylesheet that builds on main fails; Chromium 156 compares the output with the input rule by rule (CSSOM, then computed values on a sized element in a standards-mode document, colors as painted pixels in sRGB and P3). The comparison has 195 control pairs that must read equal or different. For stylesheets that read differently on both builds, mostly because of lowering, the sets of differences were compared; the three new ones are two minifier fixtures that are wrong on both and one comparison artifact.
• CSS modules are checked for consistency instead, since hashed names defeat the comparison: every reference points at a name the output defines, every export exists.
• Bun.color: 59 inputs in 13 formats on both builds; every changed cell was read.