#7777391 Plans 2023: Implement responsive UI on the plan comparison grid

Proposed Changes

This adds the styling needed to make the Plan comparison grid responsive.

Figma design: 2ee4e-pb

Testing Instructions

• Go to /start/onboarding-2023-pricing-grid/plans
• Cycle through different window sizes (ex. 375px, 880px, 1500px)
• Plans comparison grid should match the designs in Figma

NOTE: The Feature group expand/collapse feature on mobile hasn’t been implemented yet.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?

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