@Pavel can i give you admin info to check? :)
Hi. I'm not a member of the joomshaper team. But besides this, access is not needed. It is enough to use the code inspector. And I see that you did not correctly add this code. The CSS class field in the addon is not intended for the code, but simply for the name of your unique class. Add something like my-news-carousel there and use this name in the code.
.my-news-carousel .sppb-addon-article.item {
display: flex !important;
}
The code should be inserted into the custom.css file. Check the Helix documentation on this.