We use .less files (due to the fact we use antd and we have to use Less to modify it), and just use webpack import's to import them. After we build our app, we have .html files that includes all stylesheets. This file is then used as a template on the server.

If you want to use styled-components on the server you have to wrap your entire application in ServerStyleSheet collector that would collect all of your styles from components. After it's done you can just retrieve normal style tags from it and add it to your page. Take a look here: https://www.styled-components.com/docs/advanced#server-side-rendering