Remove styled-components from CheckboxGroup.dev.stories.tsx

[Copilot]

This PR removes styled-components usage from CheckboxGroup.dev.stories.tsx by migrating from the sx prop to CSS modules, following the established migration pattern used in other components.

Changes Made

• Removed all sx prop usage: Converted sx styles on CheckboxGroup, CheckboxGroup.Caption, and CheckboxGroup.Label to CSS classes
• Created CheckboxGroup.dev.module.css: Added CSS module with equivalent styles using CSS custom properties for design tokens
• Updated story metadata: Removed sx from excluded controls since it's no longer used
• Renamed story: Changed from SxProps to WithCss to reflect the new CSS-based approach

Technical Details

The migration preserves all original styling:

• CheckboxGroup: Default text color with 16px vertical margins
• Caption: Muted text color with small font size and weight
• Label: Default text color with 14px font size and medium font weight

All styles now use CSS custom properties (e.g., var(--fgColor-default), var(--base-size-16)) to maintain consistency with the design system.

Visual Verification

The CheckboxGroup dev story continues to display correctly with identical visual appearance, now using CSS modules instead of styled-components.

This change contributes to the ongoing migration away from styled-components in the Primer React codebase, improving performance and reducing bundle size.

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[changeset-bot]

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Latest commit: 37a44a2

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	90.15 KB (0%)
packages/react/dist/browser.umd.js	90.34 KB (0%)