How can I get numbered classes on rows?
In Drupal 7 and 8 the add view row classes is check-marked by default.

The problem is that in Drupal 8, it does not work. (looks like this is a bug)

As you can see in the above picture, the number is missing on the div class.
Luckily, there is a workaround solution.
In FIELDS, add Global: View result counter and hide it from display
In FORMAT, click on Settings (the 1st one)
For row class, put for example: hello-{{ counter }} and uncheck-mark &quot;add view row class&quot;, as you don't need it.

Result