Cell borders in Numbers

I inherited a Numbers spreadsheet with borders that I need to maintain. Adding a row copies some formatting that I don't want (two rows together should have top and bottom borders, not borders on each row). How do I fix this? I spent years using Excel; no flamewars please, but it is easy to do what I want in Excel. Looking for help has not been useful; Google searches turn up answers for 15 year old versions of Numbers, but not for the current (13) version.

Tell me there's an easy way to do this.