fix(accordion): add default expand icon for AccordionSummary

[ajirthan]

Purpose

Accordions previously had no default disclosure icon, so headers looked like static text and were hard to discover as expandable (#514).

This PR:

• Sets a theme-default expandIcon (ChevronDown) on MuiAccordionSummary, with medium font weight and hover styles for clearer hierarchy
• Updates Accordion Storybook stories with id / aria-controls, docs notes, an explicit ChevronDown expandIcon story, and a Plus/Minus custom expand-icon story

Related Issues

• Fixes Accordions doesn't look collapsible #514

Related PRs

• N/A

Checklist

• Followed the CONTRIBUTING guidelines.
• Manual test round performed and verified.
• Documentation provided. (Add links if there are any)
• Unit tests provided. (Add links if there are any)
• Storybook stories updated/added (if applicable)

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines?
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets?

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: d4a1629f-a0ad-4654-9365-32c7a8ef931b

📥 Commits

Reviewing files that changed from the base of the PR and between 2c0e9ac and ebbf9a0.

📒 Files selected for processing (2)

• packages/oxygen-ui/src/styles/OxygenThemeBase.test.tsx
• packages/oxygen-ui/src/styles/OxygenThemeBase.ts

📝 Walkthrough

Walkthrough

AccordionSummary now has a default ChevronDown icon, medium font weight, and hover styling in the Oxygen theme. Accordion Storybook examples add explicit id and aria-controls attributes, document expand-icon behavior, and introduce examples for explicit and custom icons. The custom example controls expansion state and switches between Plus and Minus icons while disabling default wrapper rotation.

Sequence Diagram(s)

sequenceDiagram
  participant Storybook
  participant OxygenThemeBase
  participant AccordionSummary
  participant ReactState
  participant ExpandIcons
  Storybook->>OxygenThemeBase: Load Accordion theme defaults
  OxygenThemeBase->>AccordionSummary: Set ChevronDown expand icon
  Storybook->>AccordionSummary: Render accessible summary and panel associations
  Storybook->>ReactState: Track custom expansion state
  ReactState->>AccordionSummary: Provide controlled expansion
  AccordionSummary->>ExpandIcons: Render Plus or Minus

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Suggested reviewers: jeradrutnam

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR addresses #514 by adding a default chevron, hover/cursor styling, and ARIA/storybook updates.
Out of Scope Changes check	✅ Passed	The added storybook examples and docs are directly tied to the accordion disclosure-icon work.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly matches the main change: adding a default expand icon for AccordionSummary.
Description check	✅ Passed	The description follows the template and covers purpose, related issue, checklist, and security checks.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[sm1990]

@ajirthan shall we add unit tests for this as well

[ajirthan]

@ajirthan shall we add unit tests for this as well

Ack.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@packages/oxygen-ui/src/styles/OxygenThemeBase.ts`:
- Around line 181-187: Update the AccordionSummary `root` styling to target the
nested Typography class for `fontWeight`, using the existing medium typography
value; leave the hover background and cursor rules unchanged.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 3b0d6601-b98a-49f1-a4be-4a491629578c

📥 Commits

Reviewing files that changed from the base of the PR and between 72f8414 and 2c0e9ac.

📒 Files selected for processing (2)

• packages/oxygen-ui-docs/stories/Surfaces/Accordion.stories.tsx
• packages/oxygen-ui/src/styles/OxygenThemeBase.ts

[ajirthan]

Added unit tests for the theme-default AccordionSummary expand icon (default / override / null) in packages/oxygen-ui/src/styles/OxygenThemeBase.test.tsx.