>Cetin,
>Btw, I copied the code you sent me in a PRG and ran it. The results looks very good. Thank you!
>The problem (my problem!) is that I don't understand your code and therefore would not know how to apply it to an existing application. For example, if I wanted - first - just to change the style of command buttons.
>Another thing I don't understand in your code (again, this is me), how much your code (at run-time on the customer PC) relies on the local HTML environment.

That sample is using Material Design (a styling from Google). Probably that is the best styling on the internet (check https://material.io/design/introduction/# or the simplified https://materializecss.com). It is not something that someone would learn in a day but it is easy for building nice UI.

If you would like to style at your own, then you should learn the CSS (or SASS, LESS ...).

The code doesn't rely anything on user's local. It is getting the design and script (CSS and JS) from internet. Actually, when you are done, you could download them to your computer and bundle with your application, so user doesn't even need to be connected to internet.

PS: The sample you showed was also done with Material. Another famous ones are bootstrap and jquery UI.