We want to use the locally built version of Pure so that the [layout examples](https://purecss.io/layouts/) are always using the `main` version, previously they had used a hardcoded CDN link.
To get Docusaurus to register the css as `static`, they have to exist in the `static/` directory before the site is built. Therefore, we copy the Pure `build/` in manually and `.gitignore` them. Once Docusaurus builds, they resolve as proper CSS files.