Tutorials are working fine. You must take into account that the webpage must have access to OpenVidu Server. If you are serving the tutorial on localhost and you are running openvidu Docker container inside a VM, then you must make sure that the docker contanier is properly configured with property openvidu.publicurl and that your browser has access to that url and can connect to it. This can be related to how to run the tutorials on Windows: https://openvidu.io/docs/troubleshooting/#3-i-am-using-windows-to-run-the-tutorials-develop-my-app-anything-i-should-know
openvidu-hello-world has almost no sytles. It is design to explain the basic concepts of OpenVidu in as few lines of code as possible. You have tons of other tutorials and demos with CSSs.
If you are able to get that credentials dialog on your Firefox connecting to https://3.127.36.146:4443/, that’s good. It means you are able to connect to OpenVidu Server from it. If you want to perform a quick test in OpenVidu Server Dashboard, credentials are OPENVIDUAPP:<YOUR_SECRET> (this is not necessary).
Then you should be able to connect in openvidu-hello-world, of course changing in the JS code the IP of openvidu-server to https://3.127.36.146:4443/