What’s happening here is that the CSS and/or JS from the unkpg CDN isn’t loading correctly. A few follow up questions:
Which version of dash_core_components are you using? Check with print(dcc.__version__)
Are you working offline?
If you open up your browser’s network tab (https://developers.google.com/web/tools/chrome-devtools/network-performance/) do you see any failed requests? I suspect that there will be a failed request for unpkg.cdn. The arrows below point to the 2 requests that are made to fetch the resources for dash_core_components