I wondered if there is a better solution than to what I found without changing the html-structure
The HTML structure looks like this
.divider + .block + .block + .block + .block
.divider + .block:nth-sibling(4)
.divider + .block:nth-of-class(4)
Such a pseudo-class would not work because you are expecting it to match elements relative to a different compound selector, which is not how simple selectors work. For example, if you wrote a complex selector that only had a single compound selector with that pseudo-class (and no sibling combinators):
Would you expect this to match
.block:nth-child(4n), match nothing at all, or be invalid?
It'd be nice to be able to abridge
+ .block + .block + .block + .block and make it repeat somehow, but unfortunately due to how the selector syntax is designed, it's just not possible.