Hi,
thanks for your post!
These are table borders, and adding them should be as easy as adding this to the “Custom CSS” textarea on the “Plugin Options” screen of TablePress:
.tablepress-id-123 thead th,
.tablepress-id-123 tbody td {
border: 2px solid #ffffff;
}
The 123 needs to be changed to the ID of your table.
If that does not yet do it, please post the link to the page with the table.
Regards,
Tobias