Install it and run:
npm install
npm run startTo see different behaviour on SSR, add injectFirst to StyledEngineProvider inside server.js.
In the network tab, you'll see that the initial response with injectFirst has an empty <style data-emotion="css "></style>-tag and styles are being added to the body instead.
If you look at the preview, you'll see that the styles are off:
Now, if you remove injectFirst, you see that the style-tag is filled with styles, and the preview looks different (correct in my eyes):
