You didn’t answer.
So I’ll delete the data now.

Yes, your first idea didn’t work – but the highlight stuff works fine!
Meanwhile I found out, what causes the problem: your plugin seems to have incompatibilities with Mega Addons For WPBakery Page Builder which uses the .highlight too. I think it’s good to know for you too.

Thank you again for your awesome support!!

Ah okay, thank you!

Thank you again!
I know everything about the caching and child-theme (caching is deactivated for this page and I was using a child theme). The missing function was the !important.
Now it works!

Thanks for this quick response! 😀

You’re right!
LINK

Sorry, don’t remember.  😕

…for everyone who’s interested in the CSS code:

@media only screen and (min-width: 1201px) {
.my_inner_column_class .crp-list {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  grid-template-rows: 1fr;
}
} /* RWD Gridsystem für Related Posts am Seitenende */

@media only screen and (max-width: 1200px) {
    .my_inner_column_class .crp-list {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  grid-template-rows: 1fr;
}
}

@media only screen and (max-width: 1020px) {
    .my_inner_column_class .crp-list {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: 1fr;
}
}

@media only screen and (max-width: 768px) {
    .my_inner_column_class .crp-list {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: 1fr;
}
}

.crp-list-title {
    margin-bottom: 30px;
}

.crp-list-item-title a {
font-size: 20px;
}