Hello!
We’ve found a little bug in new OJS 3.1.2 - current cover image on main page doesn’t display properly… It’s too big!
We’ve found that, there is no .cover class in /plugins/themes/default/styles/objects/issue_toc.less (.obj_issue_toc). When we putted in that from .obj_issue_summary (2 occurrences), it works fine 
Cheers!