The issue is you’re using absolute paths to files, as Barry previously suggested may be the issue.
Twitch stores Extension files on https://EXTENSIONID.ext-twitch.tv/EXTENSIONID/VERSION/HASH/, but because of the absolute reference it’s attempting to load from the root path https://EXTENSIONID.ext-twitch.tv/.
You will need to use relative paths, ie change /static/css/main.af0a5b9d.css to static/css/main.af0a5b9d.css or ./static/css/main.af0a5b9d.css. This will need to be done for all references to other files, and can usually be handled by configuring your build process accordingly.