Functionally you wouldn’t, that would be called a decoupled CMS not a headless one. Generally speaking Strapi is designed headless in a way that adhere’s to the true meaning of headless as we don’t handle the design or layout of the frontend at all.
It could be hacked together sure but that’s not what a headless CMS should do. You could handle it much like we do for the https://strapi.io website and use components and dynamic zones to adjust the layout but that’s just the frontend reading the component structure and using the stored data to build the page structure.