UI: Default Checkbox size via var() fallback

[mirka]

What?

Start the --wp-ui-* default-via-fallback convention, converting Checkbox as the first stylesheet.

Why?

--wp-ui-* custom properties are public API. They inherit. If a component assigns the default on the class that uses the variable, that assignment overwrites any ancestor value, so consumers cannot theme from a wrapper.

#81242 is the prior instance of this, for --focus-color on outset-ring__focus.

How?

1. Delete --wp-ui-checkbox-input-size: 16px from .root. Read var(--wp-ui-checkbox-input-size, 16px) on width and use aspect-ratio: 1 for the square.
2. Document the rule under Public --wp-ui-* defaults in packages/ui/CONTRIBUTING.md.

Testing Instructions

1. Run Storybook and open Design System / Components / Form / Primitives / Checkbox / Default.
2. Confirm the control is 16px by 16px.
3. In the inspector, set --wp-ui-checkbox-input-size: 32px on a parent of the checkbox. The box should become 32px by 32px.
4. Toggle WordPress global CSS. Default size should stay 16px. The ancestor override should still apply.

Screenshots

No visual changes.

[coderabbitai]

Important

Draft PR not reviewed

Draft PRs are not automatically reviewed by default.

• Trigger a manual review

To automatically review draft PRs, update your CodeRabbit configuration:

reviews:
  auto_review:
    drafts: true

---

_{Comment @coderabbitai help to get the list of available commands.}

[github-actions]

🤖 PR meta 🤖

📦 Bundle size

Size Change: 0 B

Total Size: 8.01 MB

_{95c2913 Run}

⚡ Performance

Show the results

Client side metrics exclude the server response time.

front-end-block-theme

Metric	7e82040	trunk	% Change
timeToFirstByte	64.45 ms +14.04% -7.29%	69.5 ms +3.96% -10.86%	-7.27%
largestContentfulPaint	104 ms +3.85% -7.69%	104 ms +5.77% -1.92%	0%
lcpMinusTtfb	34.5 ms +8.55% -4.2%	36.35 ms +19.67% -10.32%	-5.09%
wpBeforeTemplate	30.17 ms +25.59% -2.82%	29.94 ms +25.68% -2.07%	0.77%
wpTemplate	29.03 ms +6.44% -6.72%	29.12 ms +3.16% -4.36%	-0.31%
wpTotal	60.47 ms +13.49% -7.16%	65.16 ms +3.61% -11.82%	-7.2%
wpMemoryUsage	7.54 MB +0% -0%	7.50 MB +0% -0%	0.46%
wpDbQueries	17 +0% -0%	17 +0% -0%	0%

front-end-classic-theme

Metric	7e82040	trunk	% Change
timeToFirstByte	52.2 ms +15.9% -2.11%	53.65 ms +14.82% -4.94%	-2.7%
largestContentfulPaint	102 ms +7.84% -1.96%	100 ms +12% -2%	2%
lcpMinusTtfb	48.55 ms +0.82% -1.13%	47.6 ms +2% -3.26%	2%
wpBeforeTemplate	27.36 ms +16.23% -0.91%	27.95 ms +15.96% -3.4%	-2.11%
wpTemplate	21.71 ms +6.73% -3.22%	22.13 ms +3.52% -6.01%	-1.9%
wpTotal	49 ms +17.2% -2.12%	50.46 ms +12.49% -5.29%	-2.89%
wpMemoryUsage	6.16 MB +0% -0%	6.12 MB +0% -0%	0.58%
wpDbQueries	14 +0% -0%	14 +0% -0%	0%

media-processing

Metric	7e82040	trunk	% Change
mediaProcessingJpeg	411.13 ms +1.99% -0.67%	406.52 ms +4.52% -0.32%	1.13%
mediaProcessingAvif	6238.33 ms +0.37% -0.25%	6247.66 ms +0.21% -0.04%	-0.15%
mediaProcessingJpegToAvif	4435.96 ms +0.53% -0.17%	4435.79 ms +0.12% -0.38%	0%

media-upload

Metric	7e82040	trunk	% Change
jpegUploadProcessing	1434.64 ms +37.45% -0.93%	1431.73 ms +0.27% -0.7%	0.2%
pngUploadProcessing	231.89 ms +1.51% -7.14%	215.95 ms +3.9% -1.07%	7.38%
largeJpegUploadProcessing	1449.81 ms +1.03% -1.01%	1425.01 ms +0.47% -0.62%	1.74%
multipleImageUploadProcessing	1638.39 ms +7.14% -2.96%	1585.46 ms +9.25% -0.68%	3.34%

post-editor

Metric	7e82040	trunk	% Change
serverResponse	356.51 ms +2.54% -9.62%	346.16 ms +2.23% -8.42%	2.99%
firstPaint	170.32 ms +24.84% -10.53%	210.1 ms +40.81% -9.95%	-18.93%
domContentLoaded	995.11 ms +1.77% -0.61%	990.88 ms +1.39% -0.74%	0.43%
loaded	996.3 ms +1.76% -0.62%	991.94 ms +1.39% -0.75%	0.44%
firstContentfulPaint	329.38 ms +3% -3.47%	328.54 ms +2.89% -3.41%	0.26%
firstBlock	2671.06 ms +1.36% -1.22%	2674.85 ms +1.33% -1.21%	-0.14%
type	17.91 ms +9.77% -16.25%	16.77 ms +12.28% -18.13%	6.8%
typeWithoutInspector	15.7 ms +12.36% -20.45%	16.54 ms +10.04% -15.9%	-5.08%
typeWithTopToolbar	18.53 ms +9.88% -14.62%	19.3 ms +6.89% -17.15%	-3.99%
typeContainer	7.71 ms +3.24% -10.25%	7.29 ms +11.8% -8.64%	5.76%
focus	60.37 ms +6.06% -5.57%	62.01 ms +6.87% -4.76%	-2.64%
firstFocus	134.68 ms +0% -0%	133.08 ms +0% -0%	1.2%
selectAll	442.69 ms +2.32% -3.41%	450.79 ms +3.56% -1.13%	-1.8%
listViewOpen	51.39 ms +8.76% -6.11%	50.47 ms +11.06% -13.81%	1.82%
inserterOpen	18.49 ms +6.06% -6.44%	18.84 ms +9.71% -7.91%	-1.86%
inserterHover	2.83 ms +12.72% -2.12%	3.22 ms +9.01% -8.7%	-12.11%
inserterSearch	7.27 ms +6.19% -6.46%	6.8 ms +16.62% -10.15%	6.91%
loadPatterns	486.41 ms +4.22% -1.66%	498.67 ms +10.73% -2.78%	-2.46%
wpTotal	347.64 ms +2.36% -9.88%	337.57 ms +2.26% -8.66%	2.98%
wpMemoryUsage	13.13 MB +0% -0%	13.10 MB +0% -0%	0.22%
wpDbQueries	54 +0% -0%	54 +0% -0%	0%

site-editor

Metric	7e82040	trunk	% Change
serverResponse	422.95 ms +2.88% -6.28%	422.99 ms +1.98% -6.22%	-0.01%
firstPaint	238.43 ms +4.77% -19.18%	260.92 ms +8.3% -15.27%	-8.62%
domContentLoaded	1347.63 ms +1.83% -1.24%	1337.01 ms +0.37% -1.76%	0.79%
loaded	1348.86 ms +1.83% -1.24%	1338.2 ms +0.37% -1.76%	0.8%
firstContentfulPaint	431.4 ms +4.91% -2.49%	415.28 ms +0.75% -1.63%	3.88%
firstBlock	4162.99 ms +0.45% -0.23%	4128.7 ms +0.52% -0.24%	0.83%
type	20.2 ms +17.92% -14.41%	19.84 ms +23.39% -18.09%	1.81%
navigate	101.27 ms +12.24% -4.38%	101.45 ms +14.36% -2.7%	-0.18%
loadPatterns	1446.76 ms +8.1% -9.03%	1506.37 ms +7.06% -7.66%	-3.96%
loadPages	1180.66 ms +9.51% -8.43%	1100.03 ms +2.88% -1.56%	7.33%
wpTotal	412.54 ms +2.99% -6.47%	412.32 ms +1.97% -6.3%	0.05%
wpMemoryUsage	12.02 MB +0% -0%	11.99 MB +0% -0%	0.3%
wpDbQueries	43 +2.33% -0%	43 +2.33% -0%	0%

_{95c2913 Run}

[mirka]

I will continue to sweep the entire package after this.

[mirka]

It's becoming clearer to me that maintaining public CSS variables like this "just in case" isn't worth the cost at the moment, and is better to remove as a YAGNI. I will pivot to removal strategy (cc @WordPress/gutenberg-components).