css: parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection by robobun · Pull Request #45815 · oven-sh/bun

robobun · 2026-10-18T00:30:03Z

Problem

bun build fails on ::selection:window-inactive (Invalid selector. Invalid pseudo-class after pseudo-element) and body:window-inactive (Invalid selector. -webkit-scrollbar state found before -webkit-scrollbar pseudo-element). a:is(:window-inactive) builds as a:is().
No Bun user reported this. @theia/core 1.76.0 menus.css:95 and Tangent global.css:186 fail.
lookup_non_ts_pseudo_class (src/css/selectors/parser.rs:1528) files window-inactive with ten scrollbar-only states, as lightningcss does. This PR departs from it on purpose.

Fix

PseudoClass::WindowInactive is its own variant. It parses in a plain compound, after ::part(), in nested rules and in :is().
The new AFTER_SELECTION flag lets it follow ::selection. After ::before and the like it stays an error.
Correct because WebKit and Blink take the same positions (isPseudoClassValidAfterPseudoElement).
Verified: test/js/bun/css/css.test.ts (32 rows fail on main), test/bundler/esbuild/css.test.ts. Self-reviewed: 19 concerns raised, 17 addressed. Not done: see the last Downsides bullet.

Background

:window-inactive is not standard. WebKit matches it on any element of an unfocused window, Blink only on scrollbar parts and after ::selection.
SelectorParsingState is the bit set the parser fills per selector. A gate reads it to decide what follows a pseudo-element.
Considered a by-name gate exception: it keeps the scrollbar tag on a name that is not scrollbar-only.

Downsides

28 forms that Chrome 153 drops now build, such as ::-webkit-slider-thumb:window-inactive. main builds each with :hover in its place.
.c, :host(:is(:window-inactive)) {} printed .c, :host(:is()), now .c, :host(:window-inactive). Firefox drops that list.
Still fails: a scrollbar state outside a scrollbar pseudo-element (::-webkit-scrollbar { &:horizontal {} }). No engine has that rule. Maintainer: keep, delete or narrow it? (Notes)

Notes

Origin. No tracker issue reports this, in bun or in lightningcss. A probe of the selector parser against Chrome found it, and #45504 and #43078 list it as not fixed. It fails the same on 1.4.0, so it is not a regression. When a stylesheet has such a selector, the whole build fails, and bun has no option to relax that. Earlier selector fixes of this kind: #33151 (found by a fuzzer) and #42779 (lets :only-child follow a view transition pseudo-element, as in Chromium, through the same gate).

Real stylesheets (bun build on release builds of main and of this PR).

@theia/core 1.76.0, src/browser/style/menus.css:95: #theia-top-panel:window-inactive, #theia-top-panel:-moz-window-inactive. main exits 1 with the scrollbar message. This PR builds it. index.css:122 has body:window-inactive, body:-moz-window-inactive.
suchnsuch/Tangent global.css:186: .light ::selection:window-inactive. main exits 1. This PR builds it.
kwhorne/elyra-conductor src/app.css left ::selection:window-inactive out, because the same table row in lightningcss failed its build.

What each sheet gains.

::selection:window-inactive has an effect in Chromium, Electron and Safari.
body:window-inactive has an effect in Safari only. In Chromium it parses and matches nothing.
The two Theia lists pair the name with :-moz-window-inactive. As written, each engine drops the whole list. The list split (below) prints two rules, so the rule becomes live in Safari and in Firefox.

Browser facts. Chrome 153.0.8010.52 (new CSSStyleSheet().replaceSync(...)) keeps :window-inactive in a plain compound, after ::selection, after ::part(), after the scrollbar pseudo-elements, in nested rules, and as an argument of :is(), :where(), :not() and :has() in those positions. It drops it after ::before, ::after, ::first-line, ::first-letter, ::marker, ::placeholder, ::backdrop, ::file-selector-button, ::cue, ::view-transition, ::view-transition-group(x), ::checkmark, ::picker-icon and ::slotted(a). The tests have an error row for each of those. WebKit and Gecko are read from source, not run: the WebKit parser has the same two arms (scrollbar parts and ::selection), and Gecko does not know the name.

The question: the ten scrollbar states.

:horizontal, :vertical, :decrement, :increment, :start, :end, :double-button, :single-button, :no-button and :corner-present are still an error outside a ::-webkit-scrollbar pseudo-element. a:is(:horizontal) still prints a:is().
Chrome 153 keeps them in a plain compound, where they match nothing. The gate arm that refuses them (InvalidPseudoClassBeforeWebkitScrollbar) exists in no engine. lightningcss has the arm, and its tests expect the error.
The form that matters is a nested rule. ::-webkit-scrollbar { &:horizontal {} } exits 1, because a nested selector is parsed without its parent. openstyles/stylus scrollbar-chrome-dark.css:24 has it, and exits 1 on main and on this PR. The same form with :window-inactive builds now.
To delete the arm is about 18 lines. It is a second departure from lightningcss, so this PR does not include it. The tests here do not pin the rule: those rows stay the skipped stubs they are on main. If the answer is "delete", I add it to this PR.

::-moz-selection. The flag is set for both spellings of PseudoElement::Selection. For a Firefox target that needs the prefix, the printer writes ::-moz-selection:window-inactive beside ::selection:window-inactive. autoprefixer 10.6.1 with its default targets writes the same pair. Chrome drops that rule, and Gecko does not know :window-inactive.

List split. is_compatible reports a bare :window-inactive as not supported by every target. So a, ::selection:window-inactive {} prints as two rules under browser targets, and .p:window-inactive{} .q{} is not merged into one list. A browser that does not know the name keeps the other rule. Three new rows test this.

Where the split does not reach. The guard (is_compatible) has two holes, and :window-inactive now reaches both. main has them for other names.

It does not read the argument of :host() or ::slotted(). This holds for every target set. main prints .u, :host(:-moz-focusring) for .u{} :host(:-moz-focusring){}, and Chrome drops that list.
The printer unwraps a single-argument :is() with no check of its argument, and the guard then judges the :is() and not the argument. This matters only with no browser targets (--target=bun, --target=node). Under the default browser targets (edge88, firefox78, chrome87, safari14) the rule is split, because chrome87 has no :is(): a:is(:window-inactive), .x {} prints .x {} and a:window-inactive {}. With --target=bun, main prints a:-moz-focusring, .x for a:is(:-moz-focusring), .x {}, and Chrome drops that list.

Input	Targets	main	PR
`.u{color:teal} :host(:window-inactive){color:teal}`	default	error	`.u, :host(:window-inactive)`
`.u{color:teal} ::slotted(:window-inactive){color:teal}`	default	error	`.u, ::slotted(:window-inactive)`
`.c, :host(:is(:window-inactive)) {color:red}`	default	`.c, :host(:is())`	`.c, :host(:window-inactive)`
`a:is(:window-inactive), .x {color:red}`	default	four rules: `.x`, `a:-webkit-any()`, `a:-moz-any()`, `a:is()`	two rules: `.x`, `a:window-inactive`
`a:is(:window-inactive), .x {color:red}`	`--target=bun`	`a:is(), .x`	`a:window-inactive, .x`
`.u{color:red} .v:is(:window-inactive){color:red}`	`--target=bun`	`.u, .v:is()`	`.u, .v:window-inactive`

A list is split only when there are browser targets, so a change in the guard alone does not fix the --target=bun list. The fix is in the unwrap rule, for every name, and it changes output that builds today (a:is(:-moz-focusring) would keep its :is()). #40464 rewrites the guard. This PR changes neither.

Choices.

::details-content and ::picker() do not set the flag, though Chrome keeps :window-inactive after both. WebKit refuses it there, and Blink takes it only through the element-backed rule that css: parse ::details-content and ::picker() like ::part() #45504 ports. With css: parse ::details-content and ::picker() like ::part() #45504 the two names parse like ::part() and take :window-inactive with no more edits. No test row pins them as errors.
PseudoElement::following_pseudo_class_state() sets the per-family bits with one exhaustive match, where two if tests ran before. A new PseudoElement variant does not compile until it is classified.
The self-review asked for the one-line comments, the list-split rows and the Downsides rows, and they are in. The two concerns not done ask to delete the gate arm for the ten scrollbar states here. This PR is scoped to :window-inactive, and that arm is deliberate lightningcss behaviour, so it is the question above.

Measurements. Release builds of ff8ad61 (main when the work started) and of ff8ad61 with this change, same build directory. The last edits after that build changed comments and tests only.

Executed instructions inside parse_selector::<Selectors> per selector (qemu-x86_64 -one-insn-per-tb -d exec,nochain, (I(2000) - I(1000)) / 1000, three identical repeats):

Input	main	PR
`.c`	362	362
`.c:hover`	584	583
`.c:checked`	616	615
`a::before`	510	504
`a::before:hover`	724	718
`a::selection`	511	505
`::-webkit-scrollbar-thumb:hover`	670	665
`::view-transition-group(x):only-child`	649	641
`::part(x):hover`	627	627

parse_selector::<Selectors>: 20,775 -> 20,807 bytes, 4,313 -> 4,304 instructions, indirect jumps 9 -> 9, allocator call sites 3 -> 3. serialize_pseudo_class: 2,950 -> 2,985 bytes.
Seven functions change size, net +57 bytes. Alignment padding absorbs it: .text is 81,172,741 bytes and .rodata is 22,536,940 bytes in both builds (nm, llvm-objdump, size).
SelectorParsingState: 12 of 16 bits used (was 11), 2 bytes. size_of::<PseudoClass>(): 40 -> 40 bytes.
Differential matrix (40 pseudo-element contexts x 81 pseudo-class names x 6 wrappers through cssInternals.minifyTest): 160 of 19,440 cells change, all :window-inactive or :WINDOW-INACTIVE. That is 80 per spelling. Chrome 153 keeps 52 of the 80.

The 28 forms Chrome 153 does not keep.

6 with ::-moz-selection (bare, :is(), :where(), :not(), :has(), nested). Chrome does not know the pseudo-element.
17 after a pseudo-element bun does not know: ::-webkit-slider-thumb, ::-webkit-foo(x) and ::-webkit-slider-thumb::selection. bun passes every pseudo-class through there, except the ten scrollbar states.
3 with :has(:window-inactive) after ::selection, ::part(x) and ::part(x)::selection.
2 nested under ::cue-region and ::cue-region(b). Chrome does not know the pseudo-element.

Not fixed here.

::details-content:window-inactive and ::picker(select):window-inactive still fail. Chrome keeps them. css: parse ::details-content and ::picker() like ::part() #45504 makes them parse.
A nested rule is parsed without its parent. ::before { &:window-inactive {} } builds, as ::before { &:checked {} } does on main.
A forgiving list still drops an argument the parser refuses, with no diagnostic: ::before:is(:window-inactive) prints ::before:is().
li::before::marker still fails. Chrome keeps it.
Same on main and on this PR, and not caused by it: ::selection:hover{color:red} a{color:red} prints as one list, ::selection:hover, a. Chrome drops ::selection:hover, so it drops that list.

Overlaps.

css: parse ::details-content and ::picker() like ::part() #45504 fixes a regression and can merge first. Against this PR it has 1 conflict hunk in parser.rs (the flag list): keep HAS_PSEUDO_ELEMENT = 1 << 10 and AFTER_SELECTION = 1 << 11. Both PRs then have an exhaustive match over PseudoElement. The one that lands second can fold them into one.
css: parse :state(), ::highlight(), four css-pseudo-4 pseudo-elements, @position-try and @font-feature-values #42918 also takes bit 1 << 11 and edits the same gate condition: 3 conflict hunks in parser.rs. One of the two moves to 1 << 12. The exhaustive match does not compile until its 5 new PseudoElement variants are classified.
css: use :is() for a nesting parent with a pseudo-element when more follows the & #43078 (nesting printer, selector.rs) does not conflict. By its description, a pseudo-class after & under a pseudo-element parent prints as before, so ::selection { &:window-inactive {} } still lowers to ::selection:window-inactive.
css: keep incompatible selectors that fail the same way in one rule #40464 and css: keep a selector list whole when a member is vendor prefixed #42100 rewrite is_compatible. As written, both leave :window-inactive not supported, so the split rows hold.
Draft bun:dom and the Vitest work in one tree (not for merging) #45415 has exhaustive PseudoClass matches in src/css/selectors/dom.rs. They need one arm for WindowInactive.

Tests.

Debug build: test/js/bun/css/css.test.ts 1362 pass, test/bundler/esbuild/css.test.ts 57 pass. test/js/bun/css/ and test/bundler/css/ together: 2742 pass, 4 fail. The 4 are the css-fuzz.test.ts tests. They pass their 5 s and 10 s limits on a release build only (5 pass there, on main and on this PR).
Release build of main (ff8ad61): css.test.ts 32 fail, and the bundler case fails. Release build with this change: 0 fail.
The ten rows for the scrollbar states were skipped stubs that listed window-inactive as an error. That name is gone from the list.

…t after ::selection The name table filed `:window-inactive` with the ten scrollbar-only states. So it was an error outside a `::-webkit-scrollbar` pseudo-element, and a forgiving list such as `:is()` dropped it with no diagnostic. WebKit and Blink also take it in a plain compound, after `::selection` and after `::part()`. `PseudoClass::WindowInactive` is now its own variant. The new `SelectorParsingState::AFTER_SELECTION` flag lets it follow `::selection`. `PseudoElement::following_pseudo_class_state` sets the per-family flags with one exhaustive match. The ten scrollbar-only states stay restricted.

robobun · 2026-10-18T00:30:14Z

^{Updated 8:05 PM PT - Oct 17th, 2026}

❌ @robobun, your commit ec7373f has some failures in Build #127843 (All Failures)

🧪 To try this PR locally:

bunx bun-pr 45815

That installs a local version of the PR into your bun-45815 executable, so you can run:

bun-45815 --bun

robobun · 2026-10-18T00:30:23Z

Status

This change landed on main in #47025 (7942008). This PR is closed.

The repro, which failed on main at ff8ad61 and on 1.4.3:

printf '::selection:window-inactive { color: red }\n' > t.css && bun build ./t.css
# was: exit 1, error: Invalid selector. Invalid pseudo-class after pseudo-element

printf 'body:window-inactive { color: red }\n' > t.css && bun build ./t.css
# was: exit 1, error: Invalid selector. -webkit-scrollbar state found before -webkit-scrollbar pseudo-element

printf 'a:is(:window-inactive) { color: red }\n' > t.css && bun build ./t.css
# was: exit 0, prints a:is()

On a debug build of main at 7942008 all three build and print the selector as written, and test/js/bun/css/css.test.ts passes (2018 pass, 0 fail). #47025 also lets the ten scrollbar states parse in a plain compound and in a nested rule, which settles the question this PR asked.

coderabbitai · 2026-10-18T00:35:33Z

Walkthrough

The CSS selector parser and serializer now handle :window-inactive as a standalone pseudo-class. Tests cover its use after selection pseudo-elements and scrollbar pseudo-classes, along with minification and browser prefixing.

Changes

Window-inactive selector handling

Layer / File(s)	Summary
Parsing and serialization `src/css/selectors/parser.rs`, `src/css/selectors/selector.rs`	The parser maps `window-inactive` to `PseudoClass::WindowInactive` and tracks which pseudo-classes may follow selection pseudo-elements. It also permits `:window-inactive` after WebKit scrollbar pseudo-classes. The serializer emits it as `:window-inactive`.
Selector and bundler coverage `test/js/bun/css/css.test.ts`, `test/bundler/esbuild/css.test.ts`	Tests cover selector parsing, minification, prefixing, selector-list handling, and invalid placements for `:window-inactive` and scrollbar-state pseudo-classes.

Suggested reviewers: jarred-sumner

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to ec737

Firefox 60 will not match the generated inactive-window selector. Correct its Firefox-targeted spelling before merging, or explicitly accept that compatibility gap.

Pre-merge checks: 4

Check name	Status	Explanation
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Title check		The title clearly summarizes the main change: parsing `:window-inactive` as an ordinary pseudo-class and allowing it after `::selection`.
Description check		The description is comprehensive. It explains the problem, implementation, scope, limitations, affected cases, and verification results. It does not use the exact template headings, but it covers both…

Full details: Description check

Explanation

The description is comprehensive. It explains the problem, implementation, scope, limitations, affected cases, and verification results. It does not use the exact template headings, but it covers both required topics: what the PR does and how the change was verified.

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Inline comments:
Review comments at @src/css/selectors/selector.rs:
- Line 1133: Update the PseudoClass::WindowInactive serialization branch to emit
Firefox’s supported -moz-prefixed selector for Firefox targets, and adjust the
corresponding Firefox-targeted expectation in the test. Preserve the existing
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src/css/selectors/parser.rs
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claude

Beyond the inline findings, I also checked the following_pseudo_class_state() refactor against the two helpers it replaces — every PseudoElement variant lands in the same bucket as before (the seven ::-webkit-scrollbar* variants, the five ::view-transition-*(…) variants; bare ::view-transition stays unflagged as it was), and inserting S::empty() is a no-op. The new AFTER_SELECTION clause in parse_simple_pseudo_class is live: is_user_action_state() does not include WindowInactive, so that clause is the only path that admits ::selection:window-inactive. The only exhaustive match over PseudoClass variants outside the parser is the serializer, which gained the matching arm.

Extended reasoning...

The change moves :window-inactive out of the scrollbar-only pseudo-class enum into a top-level PseudoClass::WindowInactive, adds an AFTER_SELECTION parser-state bit, and replaces two boolean pseudo-element helpers with one exhaustive match in src/css/selectors/parser.rs, plus a serializer arm in selector.rs and tests. No security-sensitive surface is touched. Inline findings on list-splitting/:is() unwrapping behavior and the pre-existing nested scrollbar-state error remain, so a human should weigh those; the refactor itself and the gating logic were checked for behavior preservation and liveness.

Findings marked 🟡 are optional suggestions and need no follow-up push.

Additional findings (outside the current diff — GitHub can't attach inline comments there):

🔴 src/css/selectors/selector.rs — Firefox users lose styling for every selector that shares a rule with :is(:window-inactive); the base branch kept them styled. The printer unwraps a single-argument :is() unconditionally at selector.rs:865, and is_compatible at selector.rs:350-353 still reports the wrapped form compatible, so a:is(:window-inactive), .x {} (or .u{} .v:is(:window-inactive){} after merging) is emitted as a:window-inactive, .x. Gecko does not know the name and drops the whole list. On base the name failed inside the forgiving list and printed as a:is(), .x, which Firefox accepts. Fix: do not unwrap, or treat as incompatible, an :is() whose only argument is a selector is_compatible rejects, so the forgiving wrapper the author relied on survives.

Why this was flagged

Any stylesheet that wraps :window-inactive in :is() for forgiveness, built with default bun build or browser targets, then loaded in Firefox. parser.rs:1528 now returns PseudoClass::WindowInactive instead of erroring, so the forgiving list keeps it. selector.rs:1667 should_unwrap_is is true for the one simple argument, and selector.rs:865 serializes it bare. selector.rs:350 only continues when the inner list is compatible; otherwise it breaks to F::IsSelector, which Chrome/Firefox targets satisfy, so the list is neither split at rules/mod.rs:692 nor refused a merge. Output a:window-inactive, .x is dropped entirely by Gecko, so .x is unstyled. On the base commit the same input printed a:is(), .x (author's own table shows .u, .v:is()), valid in every browser. The dismissal called this pre-existing, but no name previously reached this unwrap in a form a major engine rejects; the PR introduces the first. Remedy: in should_unwrap_is or the Is arm of is_compatible, keep the :is() wrapper when the single argument is itself incompatible.

Verification: src/css/selectors/parser.rs:1528 now maps b"window-inactive" => P::WindowInactive, so the forgiving :is() keeps it. selector.rs:348-354 reports :is(:window-inactive) compatible via F::IsSelector, so nothing is split and the merge at rules/mod.rs:1150-1190 proceeds. selector.rs:863-867 unwraps unconditionally, emitting a:window-inactive, .x {}; Gecko drops the whole rule, whereas base emitted a:is(), .x {}.
🟡 src/css/selectors/selector.rs — Firefox users silently lose a sibling rule's styles, where the base failed the build with an error. With .u{color:teal} :host(:window-inactive){color:teal} under browser targets, is_compatible at selector.rs:364 maps Component::Host(_) to F::Shadowdomv1 without looking at the argument, so the rule is deemed compatible and merged into .u, :host(:window-inactive). Firefox drops the whole list and .u is unstyled. The same holds for ::slotted(:window-inactive). Fix: recurse into the :host() and ::slotted() argument in is_compatible so a selector carrying an unsupported pseudo-class is split out instead of merged. [also at: src/css/selectors/parser.rs:3716 - Firefox silently drops a merged rule and the neighbouring selector loses its style, where the base branch failed the build loudly.]

Why this was flagged

Input: .u{color:teal} :host(:window-inactive){color:teal} or the ::slotted(:window-inactive) form, minified with a browser target through bun build. Since parser.rs:1528 now yields PseudoClass::WindowInactive, the selector parses; selector.rs:364 returns F::Shadowdomv1 for Host() and Slotted() and never inspects the inner compound, so is_compatible returns true. merge_style_rules at rules/mod.rs:1168 appends the selector to the previous rule, producing .u, :host(:window-inactive). Gecko does not implement :window-inactive, so it discards the entire rule and .u loses its declaration. On the base the parser raised Invalid pseudo-class ... before -webkit-scrollbar pseudo-element and the build stopped, so no user shipped broken output. Remedy: make is_compatible recurse into Host/Slotted arguments (or return false for them when the argument contains an unsupported pseudo-class).

Verification: Pre-existing hole in untouched is_compatible, newly reachable through one more name this PR makes parseable. src/css/selectors/parser.rs:1528 makes the selector parse where the base errored. src/css/selectors/selector.rs:364 never recurses into the argument, so :host(:window-inactive) is reported compatible; src/css/rules/mod.rs:1168 then appends its selector to the previous rule, printing .u, :host(:window-inactive).
🟣 src/css/selectors/parser.rs — pre-existing: a nested rule such as ::-webkit-scrollbar { &:horizontal {} } still fails the whole build after this PR, while the sibling &:window-inactive form now builds. The InvalidPseudoClassBeforeWebkitScrollbar arm at src/css/selectors/parser.rs:3716 fires because a nested selector is parsed with a fresh state, so the parent's ::-webkit-scrollbar is never seen. Fix: the ten scrollbar states must parse when the compound carries a nesting selector (skip the arm when AFTER_NESTING is set), or drop the arm, which no browser engine has; the PR text leaves this as an open question but ships the asymmetry.

Why this was flagged

Input: a stylesheet with ::-webkit-scrollbar { &:horizontal { width: 8px } }, fed through bun build or Bun.build. The nested rule's selector list is parsed by GenericSelectorList::parse at src/css/selectors/parser.rs:1631 with SelectorParsingState::empty(), so AFTER_WEBKIT_SCROLLBAR is never set from the parent. :horizontal reaches parse_simple_pseudo_class and falls to the third branch at src/css/selectors/parser.rs:3716, where is_valid_before_webkit_scrollbar (src/css/selectors/parser.rs:1099) returns false for PseudoClass::WebkitScrollbar(_), raising "-webkit-scrollbar state found before -webkit-scrollbar pseudo-element" and failing the build. The base branch fails identically; the PR moves only window-inactive out of this gate (src/css/selectors/parser.rs:1528), so ::-webkit-scrollbar { &:window-inactive {} } now builds (tested at test/js/bun/css/css.test.ts:5460) while the ten remaining scrollbar states in the same nested position still abort.

Verification: pre-existing; acknowledged in diff. Nested rule preludes are parsed with a fresh state: src/css/css_parser.rs:1954-1960 calls SelectorList::parse_relative, which at src/css/selectors/parser.rs:1647 does let mut state = SelectorParsingState::empty();. & only inserts AFTER_NESTING (parser.rs:710-712), so :horizontal falls to the third branch at parser.rs:3716-3720. The base branch fails this input by the same route.

robobun · 2026-10-18T00:48:31Z

Answers to the three findings in the review above. I checked each one on release builds of main and of this PR.

1. Single-argument :is() (red). One part holds, and two do not.

It does not happen with a default bun build. The default browser targets include chrome87, which has no :is(), so the rule is split. a:is(:window-inactive), .x {} prints .x {} and a:window-inactive {}, and .u{} .v:is(:window-inactive){} stays two rules.
:window-inactive is not the first name to reach this. With --target=bun, main prints a:-moz-focusring, .x for a:is(:-moz-focusring), .x {}, and does the same for :-moz-window-inactive, :popover-open and an unknown name. Chrome 153 drops each of those lists.
What holds: with no browser targets (--target=bun, --target=node), a:is(:window-inactive), .x {} printed a:is(), .x on main and prints a:window-inactive, .x here.

The cause is in two places. The printer unwraps :is(X) with no check of X (selector.rs:865), and is_compatible then judges the :is() and not X (selector.rs:350). A change in is_compatible alone does not fix the list above, because a list is split only when there are browser targets. The fix is in the unwrap rule, for every name, and it changes output that builds today (a:is(:-moz-focusring) would keep its :is()). I did not put that in this PR. The description now has the full table under "Where the split does not reach".

2. :host() and ::slotted() (optional). Correct, and it is the second Downsides bullet. The guard does not read the argument for any name: main prints .u, :host(:-moz-focusring) for .u{} :host(:-moz-focusring){}, and Chrome drops that list. #40464 rewrites that guard.

3. Nested scrollbar states (pre-existing). This is the open question in the description. Both fixes are small:

Delete the arm (about 18 lines). This also fixes a:is(:horizontal), which prints a:is().
Skip the arm when the selector has &. This keeps the error for a flat a:horizontal. It would also admit .a { &:horizontal {} } and & .b:horizontal, because the & bit is set for the whole selector.

I recommend the first. I add the one a maintainer picks.

@mikamikasuki

### 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 (#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 (#33684). - Material Components, daisyUI, DocSearch, plyr: a `var()` size loses to its own fallback (#42101). - nextra, daisyUI, CKEditor: declarations written after a nested rule are moved above it (#45462). - antd 4, purecss, govuk-frontend: browser hacks in selector lists start to apply everywhere (#42100). - foundation-sites, flatpickr, 98.css, blueprintjs, scalar, react-datepicker: the build fails on valid CSS (#46756, #38552, #38534). tachyons, handsontable: it fails on the IE star hack (#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 (#46759). - hint.css and 42 more: `z-index: 1000001` and `1000000` become the same number (#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` (#41993). #### Behavior changes to look at first 1. **`light-dark()` is kept as written at 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** (#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(...)`** (#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** (#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 (#46756): `(min-width:0\0)`, `(not(hover))`. 6. **Declarations after a nested rule stay where they were written**, as 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 (#45945, #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 (#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 (#40369) and add a `cssTarget` option (#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 (#45814): 1,116 real stylesheets lack a prefix they need at the default targets. And for `backdrop-filter` (#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, #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()` (#45945). 1,164 real stylesheets - 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` (#46759). 316 real stylesheets - 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 (#46861). 171 real stylesheets - 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 (#46733). 31 real stylesheets - 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 (#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 (#45560). 2 real stylesheets - Do not merge style rules in a stylesheet that holds `revert-rule` (#46953). 1 real stylesheets - `@import ... supports(-webkit-mask: none)` kept its prefix (#38589) **Properties and shorthands** - 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 (#38583). 1,452 real stylesheets - 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 (#38582). 89 real stylesheets - 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 (#42101). 26 real stylesheets - 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 (#46882). 6 real stylesheets - 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 (#45143). 2 real stylesheets - 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` (#42022). 2 real stylesheets - 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 (#46606) - 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` (#42072) - `border; border-image: <gradient>; border-image-slice: 1` lost the gradient in every default build (#42018) - A prefixed `linear-gradient` keeps its direction, written or generated: the prefixed syntax names the starting side and measures angles differently (#46697) **At-rules** - Print @font-face format() keywords as strings (#37979). 439 real stylesheets - Print @supports `not` conditions without a leading space (#38559). 88 real stylesheets - Reset after the number token of a unicode-range (#45835). 33 real stylesheets - 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 (#46806). 18 real stylesheets - 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 #46692). In a CSS module the name now stays global, like the `list-style` that refers to it (#33679). 9 real stylesheets - 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 (#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 (#46869). 2 real stylesheets - Accept a name-only `@container` and a `style()` feature with no value (#46689). 1 real stylesheets - Parse `<timeline-range-name> <percentage>` keyframe selectors (#45652) - Allow `or` inside parentheses after a media type (#45088) - Print the `=` comparison in media and container queries as `=` (#45071) - Parse the @font-palette-values font-family descriptor as a list of family names (#45484) **Selectors** - Never wrap a selector list in :is() (#46787). 414 real stylesheets - 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 (#42100). 42 real stylesheets - 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 (#43047). 8 real stylesheets - `@scope`: `&` and implicit selectors compile to `:where(:scope)`, relative selectors and bare declarations parse (#43165). 7 real stylesheets - 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 (#43146). 2 real stylesheets - `[xl|href$=".pdf"]` lost its namespace prefix (#45159). 2 real stylesheets - Match An+B keywords exactly and take only `+` as the leading sign (#42953). 1 real stylesheets - Parse ::details-content and ::picker() like ::part() (#45504). 1 real stylesheets - 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 (#41575) - `li::before::marker` failed the build (#45810) - `&` inside `:nth-child(... of S)` is resolved when nesting is compiled away. The second selector serializer (326 lines) is deleted (#43024) **Colors and `Bun.color`** - 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 (#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 (#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 (#45362). 31 real stylesheets - 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 (#38535). 7 real stylesheets - 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) (#38487). 4 real stylesheets - Match named colors without regard to ASCII case (#45092). 3 real stylesheets - 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 #45970) (#45971) - 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 (#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 (#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`) (#42104). 24 real stylesheets - 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 (#38516) - 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 (#32286) - A one-argument `min()` / `max()` around a sum printed without any function (`width:100% - 20px`) (#46145) - `round()` breaks ties upward and handles a negative step as browsers do (#45249) **CSS modules** - A CSS module exports its `@keyframes` names (`styles.spin`). Hashing is unchanged (#46720). 145 real stylesheets - A name inside `:global(...)` prints plain but was exported as `name_<hash>`, a class no rule has (also #38573) (#45487). 90 real stylesheets - Keep container names global in CSS modules (#45247). 6 real stylesheets - 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 (#45961). 4 real stylesheets - 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 (#38523) - 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 (#30784) **Tokens, `url()`, diagnostics** - The block skip stack no longer allocates on every block exit (#39533) - Report the diagnostic's line without its line breaks in position.lineText (#38342). 192 real stylesheets - 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 (#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 (#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()` (#41557). 7 real stylesheets - 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` (#45618) - 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 (#38500) - `nth-anplusb-ident.test.ts` counts heaps in a child process (#46331) - `color.test.ts` checks the ansi-16 sweep with one `expect()` (#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 (#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`; #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 (#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: #36961 (of #37979), #38478 (of #46662), #38480 (of #46733), #38482 (of #46715), #38491 (of #38500), #38508 (of #45201), #38513 (of #45362), #38573 (of #45487), #38640 (of #38500), #45525 (of #45247), #45589 (of #46756), #45970 (of #45971) - Already fixed on `main`: #38674 - Right, but for input nobody writes (0 of 10,116 stylesheets, and not new syntax): #31916, #38526, #38592, #39349, #41139, #41801, #42042, #42484, #43078, #45604, #45908, #46086, #46221, #46224, #46273, #46694, #46707, #46737, #46755, #46816, #46870, #46934 - Right or harmless, but not worth their code, their bigger output or the behavior they change: #30905, #31924, #33332, #34426, #36225, #38006, #38512, #38547, #38551, #38561, #38572, #38576, #38607, #38623, #38667, #38692, #42106, #42912, #42918, #43407, #43434, #44700, #45442, #45546, #45747, #45759, #45825, #45946, #46061, #46127, #46206 - Need a decision (see above), stay open: #40368, #40369, #44647, #44648, #45814 - Stays open: #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.

Jarred-Sumner · 2026-10-27T19:53:40Z

Landed in #47025 (7942008).

Parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection

robobun · 2026-10-27T20:50:41Z

Thanks. I checked a debug build of main at 7942008. The selectors from this PR build and print as written, and test/js/bun/css/css.test.ts passes.

One case differs from this PR. main refuses ::-moz-selection:window-inactive, and css.test.ts pins that under "selectors that Chromium drops stay errors". autoprefixer 10.6.1 with its default targets writes that selector beside ::selection:window-inactive. So a stylesheet that went through autoprefixer still fails the build on that line:

::-moz-selection:window-inactive { color: red }
::selection:window-inactive { color: red }

error: Invalid selector. Invalid pseudo-class after pseudo-element

::-moz-selection:hover builds on main. The printer also writes ::-moz-selection:window-inactive for a Firefox 60 target. The cause is the VendorPrefix::NONE compare where parse_compound_selector sets AFTER_SELECTION. If you want this case to build, say so and I open a PR.

github-actions Bot added the claude label Oct 18, 2026

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Comment thread src/css/selectors/selector.rs Resolved

claude Bot reviewed Oct 18, 2026

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Jarred-Sumner mentioned this pull request Oct 27, 2026

css: consolidate the open CSS parser fixes #47025

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Jarred-Sumner closed this Oct 27, 2026

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css: parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection - #45815

css: parse :window-inactive as an ordinary pseudo-class, and accept it after ::selection#45815
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