bugfix: fix background color of checkbox in indeterminate state

[ak4zh]

Description

Resolved an issue where the background color of the checkbox was not displaying correctly when in the indeterminate state. Adjusted the styling to ensure consistent and accurate rendering of the checkbox background color, providing a polished user interface.

Before this change:

After this change:

Checklist

Please read and apply all contribution requirements.

• This PR targets the dev branch (NEVER master)
• Documentation reflects all relevant changes
• Branch is prefixed with: docs/, feat/, chore/, bugfix/
• Ensure Svelte and Typescript linting is current - run pnpm check
• Ensure Prettier linting is current - run pnpm format
• All test cases are passing - run pnpm test
• Includes a changeset (if relevant; see above)

[changeset-bot]

🦋 Changeset detected

Latest commit: 4141fe8

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

This PR includes changesets to release 1 package

Name	Type
@skeletonlabs/skeleton	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

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
skeleton-docs	✅ Ready (Inspect)	Visit Preview	Aug 21, 2023 9:18pm