Update newsletter form to match latest Figma design

[MohamedFazil1406]

Summary

This PR updates the newsletter form to align with the latest Figma design.

Issue #317

Changes

• Updated newsletter input styling to match the design.
• Updated subscribe button styling to match the design.
• Improved spacing, sizing, and responsive layout.
• Refined placeholder, border, and focus styles for consistency.
• Updated the CHANGELOG.

Testing

• ✅ Tested on mobile, tablet, desktop, and large desktop viewports.
• ✅ Verified shared components were not negatively affected.
• ✅ yarn build completes successfully.

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[cherylli]

Hi, it seems other changes in the service branch was included in the PR. Could you see if you're able to only include buttons and input style update? If it's too complicated we could just merge this into service-dev (after we have a decision for the other PR #315

Also if it's not possible to easily update variables (just the ones used in this PR, we will slowly convert all of them) to the new ones listed in the figma. I could open another issue, to update all of them separately.