Thank you Chris for your quick response, but that's not what I mean.
As you can see in the tutorial, there are 3 columns (as in my case) but when you select a small screen, one is displayed below the other. After returning to the larger screen, there are 3 columns back.
In the solution that you propose (if I understood correctly) I have columns one below the other the whole time.
I've been doing this tutorial several times. Funny because if I choose bootstrap 3.3.7 it works just like in the tutorial. However, in version 4.0 there is a problem that I described.
In that case the question is:
What I need to change (set) additionally in bootstrap 4.0, so that it works like in 3.3.7
No Decho, what you do is choose the setting for the column size in the viewport size you need starting with small one first. The main one is set to the small size and it works it's way up (mobile first). That tells the browser how wide the columns should be at the various sizes of the viewport.
Theres a dropdown next to the Width setting of the columns in the Options panel (choosing the Gear tab). Click that and you'll see the various screen sizes. On the first one put 12 so that it's defaulting to 12. Then in your case you would put 4 into the Med size which would then make it change to 3 columns when it hits medium size screens and the rest can stay at "none". That should work for your situation.
As for the setting it so it works like 3.3.7, it doesn't work that way anymore, it's mobile first now completely so you'll need to adjust how you think about screen sizes a bit. Most of the media queries have now changed to min-width instead of the previous max-width and the default size now is the small screen instead of the large one. You may need to check into some tutorials on that as it took me a bit to get my head around it when mobile first came out as well, thankfully it didn't take me too much to get adjusted in BSS due to that already being out a while.
Thank you very much. Thanks Jo and Chris. I guess I did not understand Chris's answer. I will try to apply to your suggestions Jo. Again thank you very much.