More Space B/W Posts

I think that you can try this:

div.site-content div#content article.post {
  border-bottom: thin solid #C0C0C0;
  margin-bottom: 6rem !important;
  padding-bottom: 6rem;
}

The problem you had trying to add space might be because the theme uses the !important in its CSS which gives a declaration priority in terms of specificity. One way to override it is to declare it again on another rule but I think this is the sort of thing that makes people frown on its use.

You can change the numbers to how you want it and I just added the border to help visualize the white space. It also adds a little more separation.

I’m no expert so you might get better solutions. And you if you aren’t already, its wiser to use a child theme for these sort of edits.