Implement Full-Site Design Refresh

I already hold a finished HTML/CSS theme and now need it woven into every page of my current site. The content, links, and back-end logic stay exactly as they are; only the visual layer changes. Your job is to replace the existing layout, styles, and assets with the new files, make sure each template calls the updated CSS correctly, and confirm that everything looks identical to the supplied design across modern browsers and devices.

Deliverables
• Full integration of the supplied HTML/CSS into all live pages
• Responsive behaviour matching the provided theme
• Cross-browser QA (Chrome, Firefox, Safari, Edge) with screenshots of key breakpoints
• A brief hand-over note summarising files touched and how to revert if needed

I will provide the zipped theme and access to the current codebase as soon as we start.