In .redocly.yaml set
apiDefinitions: main: path/to/public/openapi.json
Then run npm run bundle-local && npm run start to start a local instance of the ReDoc site
npm run build: Fetches the remote openapi.json from https://app.deltateq.com/doc/api/openapi.json and builds a zero-dep static html file from that.
npm run build-local: Does the same as build but with the local openapi file
To update/change the theme edit the theme.json file, available theme options can be found at ReDoc docs
To change the html (change font, favicon etc) edit the index-template.hbs