chore: update styling guide

[TarunAdobe]

Update Styling Documentation for SWC Components

Description

This PR documents the new guidance for maintaining styles in Spectrum Web Components (SWC). It clarifies the purpose and usage of the three stylesheets associated with each component:

1. spectrum-[component].css: The base stylesheet originally from spectrum-css.
2. [component]-overrides.css: The overrides stylesheet originally from spectrum-css.
3. [component].css: The last loaded stylesheet, which serves as the SWC override stylesheet.

Additionally, it includes details about the tools/styles and theme files (s1, express, s2foundation) and updates the relevant documentation files.

Motivation and context

This change is required to provide clear and thorough styling guidance for developers working with SWC components. It addresses the confusion around the usage of multiple stylesheets and ensures that anyone can understand how to update themes and style new components effectively.

Related issue(s)

• fixes [JIRA-1234]

Screenshots (if appropriate)

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Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed at the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my 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.

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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 approved before author can update Golden Hash

Manual review test cases

• Verify that the following docs doesn't reference to spectrum-css package

  • generating-components
  • developing a component
  • Readme

• Read the new styling guide doc and verify if it does a good job explaining how to style our components without the spectrum-css dependency

• Verify yarn new package works as expected

  • Pull this branch
  • yarn && yarn build
  • yarn new package
    Note: Newly generated package should have all the files mentioned in generating-components and shouldn't depend on spectrum-css.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 69e379c

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[github-actions]

Branch preview

• Documentation Site
• Storybook

Review the following VRT differences

When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

• Spectrum | Light | Medium | LTR
• Spectrum | Dark | Large | RTL
• Express | Light | Medium | LTR
• Express | Dark | Large | RTL
• Spectrum-two | Light | Medium | LTR
• Spectrum-two | Dark | Large | RTL
• High Contrast Mode | Medium | LTR

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.

[github-actions]

Tachometer results

Currently, no packages are changed by this PR...

[castastrophe]

Looks great! I'll approve once it's pointed to the CSS-Cutoff branch.