Modern Lightweight E-Commerce Redesign for Performance

My current e-commerce site delivers its products well, yet the pages feel heavy and they fail to clear Google PageSpeed Insights with the scores I need. I want the entire front-end rebuilt into a clean, modern interface while keeping the existing logo and colour scheme intact. Everything else is open to refinement as long as the end result loads fast, looks contemporary on every device and converts shoppers smoothly.

Key objectives
• Replace the present theme with a light, standards-compliant layout that scores 90+ on both mobile and desktop PageSpeed tests.
• Preserve brand recognition by re-using the current logo and colour palette, but refresh typography, spacing and visual hierarchy for a modern feel.
• Optimise images, scripts and CSS, introduce lazy-loading where appropriate and eliminate render-blocking resources.
• Ensure every product, cart and checkout view remains fully functional and responsive down to small screens.

Deliverables
1. Fully coded theme or template files ready to drop into the existing e-commerce platform (please indicate in your proposal which stack you prefer to work with).
2. A before-and-after Lighthouse report demonstrating performance gains.
3. Brief hand-off notes so future updates don’t undo the speed improvements.

I have the template of pages in html file. So it can be used to create theme/pages.