A static HTML template is useful because everything is explicit. A Jekyll site is useful because repeated structure can be managed once.
The conversion from one to the other should preserve the design and layout while introducing maintainability. Navigation, metadata, footers, scripts, and page shells can move into includes and layouts. Content pages can stay simple.
What changes
The main change is organization. Instead of repeating the same HTML across every page, Jekyll lets the site define shared structure in one place. Blog posts live in _posts, layouts live in _layouts, and reusable fragments live in _includes.
The result is still a static site. It can be hosted on GitHub Pages, Cloudflare Pages, Netlify, or any static hosting provider.
What should stay the same
The visual identity should not change just because the build system changes. The same CSS, spacing, color treatment, cards, navbar, hero section, and footer can remain intact.
A good conversion adds publishing capability without making the original site feel like a different product.