You can easily give a row a line above or below. For that you must give the row a html class. Right click on the pink frame of a row and chose Edit HTML Class and ID, then give it a name (e.g. row-line).
Under Lay Options -> Custom HMTL & CSS add the following code:
.row-line{ border-bottom: 1px solid black; padding-bottom: 2%; }
This would generate a full width line underneath the row.