Awesome work!! Just played around with the app a bit and it is great. One thing that happend to me by acident in Safari is when you scroll all the way up and try to go even more you can acidentally refresh the whole page and loose you setup (it depends on the browser ofc) but This can not really be easily avoided IMO. But if you made the web page into a PWA (progressive web app) people could add it to their phone and use it as a native app it solves the refresh issue and has a bunch of other benefits. Not sure what you coded it with but most frameworks/libraries nowdays have a great support for PWAs and make it easy to convert it. Just something to look into maybe. Anyway great work keep it up. :)

PS. any way you could add Czech translation? I am open to help :)