I read about a new Plone UI named ‘Volto’ and created a new instance from the Github repository: https://github.com/plone/volto
I had to install node.js and yarn on my notebook. I created a new volto package with ‘create-volto-app my-volto-app’. I could build my volto app with the command ‘npm start’. This build everything and the instance is available at port 3000 of your URL, e.g. ‘http://localhost:3000’. But you need to fire up the Plone instance too with e.g. ‘bin/instance fg’ too (otherwise you will get error messages).
The screenshot above shows the Plone site within a resolution for mobile devices. The Volto app uses the Pastanaga theme and is ‘mobile first’.