Let me show you an example:

Link: http://i.imgur.com/zbol5zI.png
@media (min-width: 768px) {
.IndexPage .DiscussionListItem-title,
.UserPage .DiscussionListItem-title {
margin-right: 155px;
}
}
This code can't be find in:
vendor\flarum\core\less
Link: https://github.com/flarum/core/tree/master/less
Someone can explain me from where is changed?
Thanks!