Documents can look right in the browser, then shift when printed or saved as a PDF. Imposia is an open-source, browser-native publishing toolkit built to reduce that drift. It keeps one canonical page document across HTML/CSS pagination, preview, and native print instead of rebuilding the layout for each surface. Use it with React or its framework-neutral Core, inspect typed layout warnings, control asset loading, and export reflowable EPUB 3.3—without a server renderer.