What fonts are compatible with Poplar and are we free to use anything we want on our postcard?

Poplar can support any font in the Google Font library. To enable this, you need to import the font directly into your HTML file. If you wish to use a font that is not supported by Google Fonts, you can also host your font files in a file-hosting platform like Amazon S3, and use the CSS @font-face declaration to load the files into your HTML. You need to have the rights or license to use the font in print in order to use this declaration.