Legacy pages are imported without stylesheets. Therefore, legacy pages will live on your NationBuilder website without the CSS and customizations made on your older website. However, HTML content will be imported into the NationBuilder site.

If you are considering migrating your older site with the styles of the NationBuilder website, you might want to consider creating the pages individually through the control panel, or hire a NationBuilder architect who could potentially import those pages for you as a paid service.

Related:

How to preserve an old website