feat(accordion): remove modifiers; simplify selectors

[castastrophe]

Description

This update removes --mod-accordion-* custom property hooks per SWC-1264, see also the RFC for extensible styling. Class selectors and variants remain unchanged; stories were refreshed to match the current API.

• Remove all --mod-accordion-* custom property hooks.
• Keep existing class selectors and variants (e.g., .spectrum-Accordion--compact, .spectrum-Accordion--spacious, .spectrum-Accordion--quiet, .is-open, .is-disabled) unchanged.
• Update stories to reflect the removal of the --mod-accordion-* override layer.

Breaking change: the --mod-accordion-* override layer is removed. Consumers should set --spectrum-accordion-* variables directly where customization is needed.

Motivation and context

• Reduce API surface and ambiguity by eliminating a parallel modifier layer.
• Ensure theming consistency through Spectrum tokens.
• Simplify long‑term maintenance and documentation.

Related issue(s)

• fixes SWC-1264

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes (or confirmed existing coverage is sufficient for styling-only changes).
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

Reviewer's checklist

• Includes a GitHub Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are passing or approved

Manual review test cases

• Accordion interactions

  1. Open Storybook accordion stories.
  2. Hover, press, and focus the header.
  3. Expect header/background colors to use Spectrum tokens and match design.

• Densities and sizes

  1. Render compact, regular, spacious across S/M/L/XL.
  2. Compare spacing and typography to tokens.
  3. Expect parity with previous visuals.

• Quiet and no inline padding

  1. Apply .spectrum-Accordion--quiet and .spectrum-Accordion--noInlinePadding.
  2. Validate visual behavior matches docs.
  3. Expect no regressions.

• Disabled items

  1. Add .is-disabled to an item.
  2. Check content and header colors.
  3. Expect --spectrum-disabled-content-color to be used.

• Open state behavior

  1. Toggle item open/closed.
  2. Observe indicator rotation and content visibility.
  3. Expect unchanged behavior.

Device review

• Did it pass in Desktop?
• Did it pass in (emulated) Mobile?
• Did it pass in (emulated) iPad?

[changeset-bot]

🦋 Changeset detected

Latest commit: 902d021

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@spectrum-css/accordion	Major
@spectrum-css/bundle	Patch
@spectrum-css/preview	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

📚 Branch preview

PR #4249 has been deployed to Azure Blob Storage: https://spectrumcss.z13.web.core.windows.net/pr-4249/index.html.

[github-actions]

File metrics

Summary

Total size: 1.44 MB^*

Package	Size	Minified	Gzipped
accordion	18.81 KB	18.01 KB	2.39 KB

accordion

Filename	Head	Minified	Gzipped	Compared to base
index.css	18.81 KB	18.01 KB	2.39 KB	🟢 ⬇ 2.77 KB
metadata.json	9.24 KB	-	-	🟢 ⬇ 2.19 KB

* Size is the sum of all main files for packages in the library.
* An ASCII character in UTF-8 is 8 bits or 1 byte.

[rise-erpelding]

Did not see any regressions in accordion with these changes!

[rise-erpelding]

Love this and I'm excited to try it out!

[rise-erpelding]

👋 bye!