Finaly I managed to do as described in your thread-link. (I had no examle.html in my openhabian install)
But the HTML-page is put into an iframe with fixed height. I can change the height by
Webview url="/static/test3.html" height=1
But eg for a “link menue dropdown” I have to change the height dynamicaly.
So the best way would be to design an extra template or alter (for experiment) the original one.
There for I have to know where the template is located.
But I didn’ find the path.
I searched for files, linked in the basicUI page-sourcecode. Eg “material.min.css”- not found.
Somewhere I found a note, openhab uses map.html to generate, but I didn’t find this ether on my raspPi.