Add scrollbar-gutter-* utilities

[RobinMalfait]

This PR adds new scrollbar-gutter-* utilities. The API looks like this:

Class	CSS
scrollbar-gutter-auto	scrollbar-gutter: auto
scrollbar-gutter-stable	scrollbar-gutter: stable
scrollbar-gutter-both	scrollbar-gutter: stable both-edges

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the change is additive, experimental-gated, and all affected snapshots are updated.

The new utilities are minimal static declarations with correct CSS values, gated behind the same experimental flag as the rest of the scrollbar utilities. The property-order additions explain all snapshot ordering changes, tests cover valid and invalid inputs, and no existing behavior is modified.

No files require special attention.

_{Reviews (4): Last reviewed commit: "Add `scrollbar-width` and `scrollbar-col..." | Re-trigger Greptile}

[greptile-apps]

The other scrollbar-* CSS properties (scrollbar-width and scrollbar-color) are used by the already-existing scrollbar-auto/thin/none and scrollbar-thumb/track utilities but are absent from this file. While that's a pre-existing gap, touching this file is a good opportunity to add them for consistent sort ordering across all scrollbar utilities.

Suggested change

	'scrollbar-gutter',
	'list-style-position',
	'scrollbar-gutter',
	'scrollbar-width',
	'scrollbar-color',
	'list-style-position',

[RobinMalfait]

Added a separate PR for this: #20019

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 5103eeee-779d-4c62-848d-5e55cc0a4e4b

📥 Commits

Reviewing files that changed from the base of the PR and between aa9a310 and d2225f1.

⛔ Files ignored due to path filters (1)

• packages/tailwindcss/src/__snapshots__/intellisense.test.ts.snap is excluded by !**/*.snap

📒 Files selected for processing (6)

• CHANGELOG.md
• packages/tailwindcss/src/compat/config.test.ts
• packages/tailwindcss/src/compat/plugin-api.test.ts
• packages/tailwindcss/src/property-order.ts
• packages/tailwindcss/src/utilities.test.ts
• packages/tailwindcss/src/utilities.ts

✅ Files skipped from review due to trivial changes (3)

• packages/tailwindcss/src/compat/config.test.ts
• packages/tailwindcss/src/property-order.ts
• CHANGELOG.md

🚧 Files skipped from review as they are similar to previous changes (2)

• packages/tailwindcss/src/utilities.ts
• packages/tailwindcss/src/utilities.test.ts

---

Walkthrough

This PR adds support for the CSS scrollbar-gutter property to Tailwind CSS. Three new utility variants—scrollbar-gutter-auto, scrollbar-gutter-stable, and scrollbar-gutter-both—are introduced within the existing enableScrollbarUtilities feature flag. The property is inserted into the CSS property ordering configuration after scroll padding properties. A comprehensive test suite validates that all variants generate correct CSS output and that invalid variant forms are properly rejected.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding scrollbar-gutter utility classes to Tailwind CSS.
Description check	✅ Passed	The description directly relates to the changeset by documenting the three new scrollbar-gutter utility classes and their CSS mappings.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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