This is LibreOffice Online, which provides basic collaborative editing of documents in a browser by re-using the LibreOffice core. Rendering fidelity should be excellent, and interoperability match that of LibreOffice.
The configuration file of LibreOffice Online WebSocket Daemon (loolwsd) is at /etc/loolwsd/loolwsd.xml. You can copy it out from the container, tweak it, copy back and commit, as you like.
You can also pass the following environment variables to container:
By default, when the container is started, it generates a new self-signed SSL certificate, SSL CA certificate, and secret key. If you want to use your own SSL certificate, SSL CA certificate, and secret key, you can disable this.
Domain name of your WOPI host.
User name for the Admin Console.
Password for the Admin Console.