poc: Panda under the hood, Gamut's styling API unchanged by dreamwasp · Pull Request #3405 · Codecademy/gamut

dreamwasp · 2026-08-06T18:15:43Z

What this proves

Panda CSS can generate Gamut's design tokens and its components' CSS, while every existing call site keeps working exactly as written — with Emotion gone entirely, runtime and types.

A consumer changes one import plus one type-augmentation specifier.

yarn install                              # once, from repo root
yarn nx run emotion-to-gamut-poc:dev      # → http://localhost:5174

Not for merge as-is — it's a decision aid. But note it now does touch packages/ (see §8): 5 files in variance and 1 in gamut-styles — types-only apart from sheet.ts, which is spike code.

✅ The quadratic CSS-insertion defect is fixed

An earlier revision of this PR appended a text node to a <style> element per
rule, forcing the browser to reparse the whole stylesheet each time — quadratic,
1,169 ms for 2,000 rules vs 1.8 ms with insertRule.

Fixed in src/gamut/sheet.ts: one insertRule call per rule, and rejected rules
quarantined into their own <style> rather than appended to the shared one.
The engine is now at parity with Emotion on mount (1.08x), style recalculation
(1.01x) and CSS size (0.99x). §9 has the numbers.

1. What a call site changes

- import styled from '@emotion/styled';
+ import { styled } from '@codecademy/gamut-styles';

css, variant, states, styledOptions, Box, ColorMode, Background were already imported from Gamut.

2. Who does what, and why

	does what	why
Panda (build time)	every token as a CSS variable, 5 themes × 2 colour modes; static CSS for Gamut's own components	tokens and DS components are a closed set Gamut controls, so they can be enumerated ahead of time
Gamut (`variance`, runtime)	`css()` / `variant()` / `states()` / system props at call sites	consumer values are open — `width="37.5%"`, a colour from an API, a prop-driven ternary. A build-time extractor can't see them
~100 lines (`src/gamut/sheet.ts`)	style object → class name	this is all Emotion was doing. Replacing only it is why nothing else changes

The split follows from what's knowable when. variance isn't forked or reimplemented — the real @codecademy/variance and real Gamut prop config are workspace deps.

3. Theme mapping

Gamut's theme stores colours as CSS-variable references — coreTheme.colors.primary is literally 'var(--color-primary)'. variance never touches a hex; it emits the reference and something must define it. A React <Variables> component does today at runtime; Panda now does at build time.

A theme is then just different alias assignments over one palette:

theme	light `--color-primary`
core	`var(--color-hyper-500)`
admin	`var(--color-blue-500)`
platform	`var(--color-hyper-500)`
lxStudio / percipio	`var(--color-sapphire)`

Switching theme or mode is an attribute flip (data-theme / data-color-mode) — no rebuild, no style re-render. Both switchers are live on the page.

Colour mode reassigns variables rather than using selector conditions, which is what makes nesting correct: it resolves from the nearest ancestor. A descendant selector ([data-color-mode=dark] &) gets light-inside-dark wrong — the inner element matches both conditions and source order beats proximity.

4. What's demonstrated

#	Pattern	Source
1	`variant({ prop, base, variants })` + `StyleProps` + `styledOptions`	verbatim `mono/.../AppBar/AppBarSection.tsx`
2	A Panda-backed `StrokeButton` extended by the unchanged `styled(X)(css(…), states(…))` API	verbatim `mono/.../OAuthButtons/elements.tsx`
3	System props — `<Box p={16} bg="primary" />`	real prop config + scales
4	`ColorMode` / `Background`, incl. nested light-inside-dark	—
5	styled.span`…` with `${props => …}`	mono has 234

Section 2 is the proof in one component: StrokeButton's CSS is 100% Panda static output (.gmt-stroke-button--variant_primary), extended by the untouched Emotion-era API.

5. Verified mechanically

typecheck clean — including src/type-safety.test-d.tsx (see §8)
build clean — 30kB CSS, 3.46kB gzipped
jsdom: 85 variables referenced, 333 defined, 0 missing; 32 classes in DOM, 0 without a matching rule
All 5 themes × 2 modes emitted; all 4 recipe variants force-emitted via staticCss
grep '@emotion' packages/variance/src → nothing. Bundle contains no serializeStyles / insertStyles / createCache / @emotion

6. Three things found the hard way

Panda's extractor collides with Gamut's css(). Both are named css. Pointed at app source, Panda "extracts" Gamut's calls into nonsense — .bg_primary { background: primary }, .pos_left { position: left } (from variant() keys), .__43 { _: 43px } (from responsive { _: 43 }). Renders fine, but silently inflated the sheet 11kB → 27kB. Panda now scans only its own config; importMap is the real fix if a consumer wants extraction.

Root cause, identified later: this is deeper than a name clash on css. Those three outputs are each a prop-vocabulary collision between the two systems:

.bg_primary { background: primary } — Gamut's bg is backgroundColor; Panda's bg is background. Same prop, different CSS property.

.__43 { _: 43px } — Gamut's responsive base key is _; Panda's is base. (mono: 2,793 _ sites across 810 files.)

.pos_left — Panda reading variant() config keys as style props.

The consequence is a standing design constraint: Panda is the build-time CSS generator Gamut drives, not an authoring surface consumers touch. Adopting Panda's JSX factory (styled-system/jsx, <Box mt="4">) in consumer code would make these collisions load-bearing rather than incidental — and Panda's runtime derives class names without emitting CSS, so any value its extractor didn't see renders silently unstyled. See panda-via-gamut-option-b.md.

Core's palette is not a superset. lxStudio and percipio add their own tokens (--color-sapphire, --color-percipioTextPrimary, --color-lxStudioSuccess). Emitting only Core's left 33 variables dangling — which fails silently as unstyled output. Fix: emit the union plus per-theme overrides.

Dropping preset-panda more than halved the output. Its default rose/fuchsia/violet palette is dead weight for a design system with its own tokens.

7. Theme type safety with no Emotion — including in the types

⚠️ Correction to earlier revisions of this PR: I said Emotion's type anchor was "exactly two lines." That was wrong. It was four files, and one of them was variance augmenting Emotion itself:

variance/src/types/theme.ts:23           declare module '@emotion/react' { Theme extends BaseTheme }
variance/src/types/props.ts:1            import { Theme } from '@emotion/react'   (used :26)
variance/src/types/config.ts:1           import { Theme } from '@emotion/react'   (used :31,:64,:66,:79)
variance/src/utils/serializeTokens.ts:1  import { Theme } from '@emotion/react'

The insight: variance already defined its own theme types (BaseTheme, Breakpoints). It was borrowing Emotion's Theme interface purely as the mutable global registry consumers augment — Emotion did nothing with it; it just happened to be the interface everyone reached for. So variance now owns the slot:

// packages/variance/src/types/theme.ts
export interface Theme extends BaseTheme {}   // ← augment this

Consumers change the specifier only:

- declare module '@emotion/react'       { export interface Theme extends CoreTheme {} }
+ declare module '@codecademy/variance' { export interface Theme extends CoreTheme {} }

That's the whole migration for the 19 real augmentation sites (18 mono, 1 platform).

Typecheck impact: variance 0 errors, gamut-styles 0 errors, gamut 268 — and gamut is 268 on pristine main too (verified by stashing). Typecheck-neutral across the repo.

One transitional wart: gamut-styles/src/typings/theme.d.ts now declares both registries. The Emotion one stays only because gamut-styles still uses Emotion's ThemeProvider/useTheme at runtime, and those are typed by Emotion's Theme. It's deletable the moment that provider is replaced — the PoC drops it entirely. Both point at the same CoreTheme, so they can't drift.

8. Do `variant()` / `states()` still produce dependable types?

Yes — and they're structurally immune to the swap. They derive prop types from the config object you pass them, not from the theme. Theme only appears in the theme?: member:

StyleProps<typeof positionVariants>
//  = VariantProps<"position", false | "left" | "right" | "center"> & { theme?: Theme }
StyleProps<typeof toggleStates>
//  = Partial<Record<"compact" | "isFancy", boolean>>              & { theme?: Theme }

So the prop is named after prop, its values are the exact literal union of declared keys, and states are exactly the declared booleans. Only scale-valued props (p, bg, fontSize) depend on keyof Theme.

Pinned by src/type-safety.test-d.tsx — 9 negative cases where yarn typecheck is the assertion. It fails in both directions: if safety silently regressed, tsc reports Unused '@ts-expect-error' directive. I confirmed it really fails by deliberately breaking one case.

All still rejected:

css({ fontSize: 12 });     css({ p: 5 });      css({ bg: 'chartreuse' });   <Box p={5} />
{ position: 'middle' }     { variant: 'left' } { isFancy: 'yes' }           { hasBorder: true }

9. Measured in a real browser

Earlier revisions listed performance as out of scope. It is now measured in headless Chromium with CDP tracing (~/code/base camp/reboot/injector-browser-poc, which imports this branch's engine by path rather than copying it). 200 cards ≈ 1,400 styled nodes, 7 runs/arm, medians, first discarded.

scenario	arm	mount	re-render	recalc	css kB
low cardinality	emotion	32.5ms	11.3ms	1.5ms	4.0
low cardinality	engine	35.8ms	17.0ms	1.5ms	3.8
high cardinality	emotion	34.0ms	12.8ms	2.2ms	29.9
high cardinality	engine	36.8ms	19.3ms	2.2ms	29.7

Ratio to Emotion, high cardinality: 1.08x mount, 1.51x re-render, 1.01x recalc, 0.99x CSS bytes.

Parity on mount, style recalculation and CSS size. The remaining 1.51x on re-render is this branch having no tier-2 memoisation — it resolves every style function on every render, which is a separate optimisation and is deliberately out of scope here (§11).

Note the ratios are diluted by React: ~33ms of every mount number is rendering 1,400 nodes, which both arms pay. The styling delta is a larger fraction of the styling work than these ratios suggest.

The defect this found, and the fix

The first run measured 1.58x mount / 2.39x re-render. Cause: sheet.ts appended a text node to a <style> element per rule.

A <style> element has two representations — its child DOM nodes, and the parsed CSSStyleSheet the engine consults. Changing the children invalidates the parsed sheet, so the browser reparses the entire accumulated text. Appending rule n costs O(n); the sequence is O(n²).

Seven insertion strategies, same rules, live CSSOM:

strategy	100	500	2000	growth
`appendChild(createTextNode)` — the old code	3.5ms	72.0ms	1169.5ms	O(n²)
`CSSStyleSheet.replaceSync` per rule	3.1ms	75.2ms	1189.9ms	O(n²)
`<style>` per rule (Emotion's dev path)	0.4ms	1.4ms	6.3ms	O(n)
`insertRule`	0.1ms	0.5ms	1.8ms	O(n)
`insertRule` + `@layer`	0.3ms	1.1ms	2.5ms	O(n)
constructable + `insertRule`	0.1ms	0.5ms	2.0ms	O(n)
`textContent`, batched once	0.0ms	0.1ms	0.3ms	O(n), 1 write

replaceSync is the diagnostic: a constructable CSSStyleSheet has no <style> element and no document-level invalidation, yet per-rule replaceSync is equally quadratic. The cost is reparsing accumulated CSS text, not DOM mutation.

Worth noting Emotion avoids this in both modes — insertRule in production, and a fresh <style> per rule in development so each reparse covers one rule. The old code had neither escape: text nodes into a single shared sheet.

Two changes, both required:

One insertRule call per rule. cssText already builds one rule per serialized block, so ruleTexts() returns them separately and each goes in on its own call.
The fallback no longer poisons the shared sheet. It was catch { el.appendChild(document.createTextNode(payload)) } — so one throw (an unsupported at-rule, a rejected vendor prefix) put that sheet back on the quadratic curve permanently and silently. Fixing the write while keeping that catch would have left the landmine armed. A rejected rule is now quarantined into its own <style>: it still applies, it can't slow anything else down, and in dev it warns.

Deliberately no `@layer`

panda-styling-poc's engine wraps each payload in @layer gamut.consumer{…}, which is what lets a multi-rule payload through insertRule in a single call. Not done here, for two reasons:

Cascade. Emotion appends unlayered CSS, and unlayered rules beat every layered rule. Introducing a layer would silently change precedence against Panda's own @layer output.
It's slower. Measured by monkey-patching the layer approach in: 1.10x mount / 1.92x re-render / 1.46x recalc / 1.24x CSS bytes — worse than the shipped fix on every metric. It also explains a layout regression the harness had flagged as unexplained (14.7ms vs Emotion's 9.9ms; now 9.2ms vs 9.5ms).

So panda-styling-poc has the right primitive and the wrong wrapper.

Still unmeasured

Hydration — the harness is client-side createRoot only, and all six mono apps are pages-router SSR. Chromium only, one machine, synthetic tree.

10. How much runtime CSS is actually needed

The runtime tier this PR introduces is smaller than the raw call-site counts suggest. Measured across mono (read-only AST scans, codemod-poc/runtime-need*.mjs):

	occurrences	genuinely need a runtime-manufactured class
system-prop JSX attributes	21,093	161 (0.76%)
`styled()`/`css()` interpolations	424	73 (17.2%, upper bound)
combined	21,517	234 — 1.09%, in 154 files

94.5% of system-prop attributes pass a plain literal. The useful axis is closed-vs-open, not static-vs-dynamic: a computed value on a theme-scaled prop is still prebuildable, because runtime only needs to select a class rather than manufacture one. And 82.8% of style-function interpolations turn out to be variant()/states() written as control flow — boolean guards, ternaries over theme reads, switch returning fixed strings.

This refines the "47 of 126 props have a closed value space" figure used in earlier docs. That describes the prop surface, not the call-site distribution, and it counted ~28 finite CSS-keyword props (display, position, flexDirection, justifyContent, …) as open when their keyword sets are enumerable.

The consequence for reviewing this PR: for ~99% of sites the injector is a CSS-size optimisation; for the ~1% it is a correctness requirement. Nothing else can produce gridTemplateColumns={`repeat(${tickCount * 2}, 1fr)`}. Both justify the hybrid, but only the second can't be designed away — which is why the runtime tier stays.

Numbers are upper bounds (syntactic, not type-checked). mono only; front is .jsx so the globs miss it.

11. Out of scope

SSR, hydration measurement, migrating Gamut's ~109 internal styled sites to recipes, replacing Emotion's runtime ThemeProvider/Global/keyframes/css prop. Explored on cass-GMT-1715 (GMT-1715). Performance is no longer out of scope — see §9.

Reviewing this

Verification here is jsdom + CSS analysis, which is what caught both dangling-variable bugs, but it can't confirm it looks right — yarn dev closes that gap. Browser performance is covered separately by injector-browser-poc (§9); note that spike points at this branch's engine, so re-running it after the sheet.ts fix is the check that the fix worked.

Please don't benchmark this branch as-is. The unfixed quadratic write makes the approach look ~1.6x worse than it is.

🤖 Generated with Claude Code

@emotion

A minimal, self-contained Vite PoC (spikes/emotion-to-gamut-poc, 16 files, ~500 lines of engine code) showing that today's Emotion-authored Gamut API works unchanged when `styled` is imported from Gamut instead of Emotion: - import styled from '@emotion/styled'; + import { styled } from '@codecademy/gamut-styles'; Nothing else about a call site moves. css/variant/states/styledOptions/Box/ ColorMode/Background were already imported from Gamut. WHY IT WORKS: variance's css()/variant()/states() already return (props) => CSSObject and already resolve at runtime. Emotion's only real job was merging those results into a class. So only that step is replaced (src/gamut/sheet.ts, ~100 lines); the real @codecademy/variance and the real Gamut prop config are workspace deps, not forks or reimplementations. DEMONSTRATED, using code copied VERBATIM out of mono: 1. variant({ prop, base, variants }) + StyleProps + styledOptions — mono/libs/ui/brand/src/AppBar/AppBarSection.tsx 2. css() + states() composed, nested @media, responsive { _, xs } values, withComponent — mono/libs/ui/login-or-register/src/OAuthButtons/elements.tsx 3. system props on Box, through the real prop config and scales 4. ColorMode + Background, including nested light-inside-dark 5. styled.tag`...` template literals with ${props => ...} interpolation VERIFIED: typecheck clean (and token safety intact — fontSize={12} is rejected); vite build clean; the built bundle contains ZERO Emotion (serializeStyles / insertStyles / createCache / @emotion all absent); rendered in jsdom it produces 27 distinct classes and 3.8kB of CSS with @media preserved, --color-* variables emitted, and state props kept off the DOM. Colour mode reassigns CSS variables rather than using selector-based conditions, because a descendant selector gets light-inside-dark wrong — the inner element matches both conditions and source order beats proximity. ONE HONEST CAVEAT: src/gamut-theme.d.ts still augments @emotion/react. It is TYPES-ONLY (the bundle check proves nothing runtime touches Emotion). variance anchors its whole prop type system to Emotion's Theme at exactly two lines — types/props.ts:1 and types/config.ts:31 — so without the augmentation `keyof Theme` is never and every `scale: 'colors'` degrades. Adding that one file took this PoC from 20+ type errors to 1. Every mono app already has this file (18, plus 1 in platform), so it is not new work; a real migration repoints those two variance lines at a Gamut-owned registry and the 19 sites change specifier only. Out of scope on purpose, to keep it readable: static/zero-runtime CSS, SSR, performance, Global/keyframes/the css prop. Root package.json gains spikes/* in workspaces. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

…nged Reframes the PoC around the actual question: can PANDA be used without changing Gamut's external styling API? Yes, and the division of labour falls out of what's knowable when. Panda (build time) every design token as a CSS variable, for all 5 themes x 2 colour modes, + static CSS for Gamut's own components. Tokens and DS components are a CLOSED set Gamut controls, so they can be enumerated ahead of time. Gamut (runtime) css()/variant()/states()/system props at call sites. Consumer values are OPEN (width="37.5%", an API colour, a prop-driven ternary) so a build-time extractor cannot see them. ~100 lines style object -> class name (src/gamut/sheet.ts). This is all Emotion was doing; replacing only it is why nothing else changes. THEME MAPPING: Gamut's theme stores colours as CSS-variable REFERENCES — coreTheme.colors.primary is literally 'var(--color-primary)'. variance never handles a hex; it emits the reference and something must DEFINE it. A React <Variables> component does today, at runtime; Panda now does at build time. A theme is then just different alias assignments over the same palette: core->hyper-500, admin->blue-500, lxStudio/percipio->sapphire. Switching theme or mode is an attribute flip (data-theme / data-color-mode) — both live on the page. FIXES THE BLANK-PAGE BUG from the previous commit: the hand-rolled <Variables> emitted only the semantic aliases, which point at palette variables it never defined, so everything resolved to nothing. Panda emits both layers. THREE THINGS FOUND THE HARD WAY, all documented in the README: - Panda's extractor collides with Gamut's identically-named css(). Pointed at app source it emitted nonsense (.bg_primary{background:primary}, .pos_left{position:left} from variant() KEYS, .__43{_:43px} from responsive { _: 43 }) and inflated the sheet 11kB -> 27kB. Panda now scans only its own config; importMap is the real fix if a consumer wants extraction. - Core's palette is NOT a superset. lxStudio/percipio add their own tokens (--color-sapphire, --color-percipioTextPrimary, …), so emitting only Core's left 33 variables dangling — which fails SILENTLY as unstyled output. Now emits the union plus per-theme overrides. - Dropping preset-panda (its rose/fuchsia/violet palette is dead weight here) more than halved the output. VERIFIED: typecheck clean with token safety intact (fontSize={12} rejected); build clean at 30kB CSS / 3.46kB gzipped; in jsdom 85 variables referenced / 333 defined / 0 MISSING, and 32 classes in the DOM / 0 without a matching rule. Section 2 of the demo is the proof in one component: StrokeButton's own CSS is 100% Panda static output, extended by the untouched styled(X)(css(…), states(…)) API copied verbatim from mono. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

codecademydev · 2026-08-06T19:37:39Z

📬 Published Alpha Packages:

Package	Version	npm	Diff
`@codecademy/gamut`	`72.5.2-alpha.87f6e9.0`	npm	diff
`@codecademy/gamut-icons`	`9.57.12-alpha.87f6e9.0`	npm	diff
`@codecademy/gamut-illustrations`	`0.58.17-alpha.87f6e9.0`	npm	diff
`@codecademy/gamut-kit`	`3.0.15-alpha.87f6e9.0`	npm	diff
`@codecademy/gamut-patterns`	`0.10.36-alpha.87f6e9.0`	npm	diff
`@codecademy/gamut-styles`	`20.1.1-alpha.87f6e9.0`	npm	diff
`@codecademy/gamut-tests`	`6.0.7-alpha.87f6e9.0`	npm	diff
`@codecademy/variance`	`0.26.2-alpha.87f6e9.0`	npm	diff
`eslint-plugin-gamut`	`2.4.4-alpha.87f6e9.0`	npm	diff

github-actions · 2026-08-06T19:43:50Z

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@emotion

…endency Answers "how do we get theme type safety without the Emotion declaration, and do variant()/states() still produce dependable types?" — yes to both, proven. CORRECTION: earlier notes (this repo's docs and PR #3405) said Emotion's type anchor was "exactly two lines." That was wrong. It was FOUR files, and one of them was variance augmenting Emotion itself: types/theme.ts:23 declare module '@emotion/react' { Theme extends BaseTheme } types/props.ts:1 import { Theme } from '@emotion/react' (used :26) types/config.ts:1 import { Theme } from '@emotion/react' (used :31,:64,:66,:79) utils/serializeTokens.ts:1 import { Theme } from '@emotion/react' THE INSIGHT: variance already defined its own theme types (BaseTheme, Breakpoints). It was borrowing Emotion's `Theme` interface purely as the MUTABLE GLOBAL REGISTRY that consumers augment — Emotion did nothing with it; it just happened to be the interface everyone reached for. So variance now owns the slot: export interface Theme extends BaseTheme {} // augment this `grep '@emotion' packages/variance/src` now returns nothing. Consumers change the specifier only — same declaration, different module: - declare module '@emotion/react' { export interface Theme extends CoreTheme {} } + declare module '@codecademy/variance' { export interface Theme extends CoreTheme {} } That is the whole migration for the 19 real augmentation sites (18 mono, 1 platform). TRANSITIONAL: gamut-styles/src/typings/theme.d.ts now declares BOTH registries. The Emotion one stays only because gamut-styles still uses Emotion's ThemeProvider/useTheme at runtime, and those are typed by Emotion's Theme. It is deletable the moment that provider is replaced — the PoC drops it entirely. Both point at the same CoreTheme so they cannot drift. TYPECHECK IMPACT: variance 0 errors, gamut-styles 0 errors, gamut 268 — and gamut is 268 on pristine main too, verified by stashing. The change is typecheck-neutral across the repo. DO variant()/states() STILL PRODUCE DEPENDABLE TYPES? Yes, and they are structurally immune to this swap: they derive prop types from the CONFIG OBJECT passed to them, not from the theme. `Theme` only appears in the `theme?:` member. StyleProps<typeof positionVariants> = VariantProps<"position", false|"left"|"right"|"center"> & { theme?: Theme } StyleProps<typeof toggleStates> = Partial<Record<"compact"|"isFancy", boolean>> & { theme?: Theme } Pinned by spikes/emotion-to-gamut-poc/src/type-safety.test-d.tsx: 9 negative cases where `yarn typecheck` IS the assertion. It fails in both directions — if safety silently regressed, tsc reports "Unused '@ts-expect-error' directive". Verified it really fails by deliberately breaking one case. Still rejected: css({ fontSize: 12 }), css({ p: 5 }), css({ bg: 'chartreuse' }), <Box p={5} />, { position: 'middle' }, { variant: 'left' }, { isFancy: 'yes' }, { hasBorder: true }. The PoC now has zero Emotion in runtime AND types; its bundle contains no serializeStyles / insertStyles / createCache / @emotion. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nx-cloud · 2026-08-06T21:11:12Z

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☁️ Nx Cloud last updated this comment at 2026-08-07 20:16:44 UTC

Closes the proof that NOTHING in Gamut requires Emotion. Everything else was already covered; these were the two remaining APIs with no demonstrated replacement. Both fall out of the serializer that already exists — they just skip the class-scoping step: injectGlobal(styles) top-level keys are REAL selectors instead of being scoped to a generated class. Backs a <Global styles={…}> component with the same call shape Gamut's own globals (Reboot, Typography, Variables) already author against. Replaces 10 references in packages/*. keyframes(frames) serialises each step, hashes the body into a name, and injects `@keyframes <name>{…}`. Returns the NAME, so it drops into either shape Emotion supports: `animationName: spin` or `animation: `${spin} 1s``. Replaces 5 references in packages/*. VERIFIED (jsdom): <Global> emits body{margin:0} UNSCOPED — no class prefix — plus the box-sizing reset; keyframes() emits a complete @Keyframes gmt-kf-10qu4pj{0%, 100%{opacity:1}50%{opacity:0.35}} and the animating element references it by name. Still 0 missing CSS variables and 0 classes without a matching rule. (My first assertion on the keyframe steps reported false — a lazy regex stopping at the first `}}` and capturing only step one. The CSS was correct; the check wasn't. Replaced with brace-matching.) README now carries the full inventory: every Emotion API Gamut uses, its site count, and its replacement. Two entries worth calling out: - createCache / CacheProvider / Options / StylisPlugin (10 sites) are replaced by NOTHING — they aren't needed. Class names are content-hashed and deterministic, so there is no per-request cache to thread. - @emotion/jest `matchers` (4 test sites) is the one genuinely unreplaced item; it asserts on Emotion-generated CSS and needs an equivalent matcher against the Gamut sheet. Straightforward, not built here. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

codecov · 2026-08-07T13:52:02Z

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…s quadratic Appending a text node to a <style> element invalidates its parsed stylesheet, so the browser reparses everything already in it. Inserting rule n therefore cost O(n) and the whole sequence O(n²): measured in headless Chromium, 1,169ms for 2,000 rules versus 1.8ms with insertRule. Two changes, both needed: - One insertRule call per rule. cssText already built one rule per serialized block, so ruleTexts() now returns them separately. - Rejected rules are quarantined into their own <style> element. The old `catch { appendChild(createTextNode(...)) }` put the shared sheet back on the quadratic curve permanently and silently on a single throw, so fixing the write while keeping that fallback would have left the landmine armed. Deliberately no @layer wrap, unlike panda-styling-poc's engine. A layer block makes a multi-rule payload legal in one insertRule call, but Emotion appends unlayered CSS and unlayered rules beat every layered rule — so a layer would silently change precedence against Panda's own @layer output. It also measured slower on every metric (1.10x/1.92x/1.46x/1.24x vs 1.08x/1.51x/1.01x/0.99x) and was the cause of a layout regression the harness had flagged. Engine is now at parity with Emotion on mount (1.08x), style recalculation (1.01x) and CSS size (0.99x). Re-render remains 1.51x, which is this branch having no tier-2 memoisation. Evidence: ~/code/base camp/reboot/injector-browser-poc Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

dreamwasp and others added 2 commits August 6, 2026 14:12

dreamwasp changed the title ~~poc: prove the Gamut styling API survives an Emotion→Gamut import swap~~ poc: Panda under the hood, Gamut's styling API unchanged Aug 6, 2026

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poc: Panda under the hood, Gamut's styling API unchanged - #3405

poc: Panda under the hood, Gamut's styling API unchanged#3405
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What this proves

✅ The quadratic CSS-insertion defect is fixed

1. What a call site changes

2. Who does what, and why

3. Theme mapping

4. What's demonstrated

5. Verified mechanically

6. Three things found the hard way

7. Theme type safety with no Emotion — including in the types

8. Do variant() / states() still produce dependable types?

9. Measured in a real browser

The defect this found, and the fix

Deliberately no @layer

Still unmeasured

10. How much runtime CSS is actually needed

11. Out of scope

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dreamwasp commented Aug 6, 2026 •

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8. Do `variant()` / `states()` still produce dependable types?

Deliberately no `@layer`

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