.anvil-data-row-panel>.data-row-col {
border: 1px solid #888 !important;
}
it’s not perfect but it’s simple
if you only want this while printing you can create a role for your datagrid
self.data_grid.role = 'datagrid-printable'
.anvil-role-datagrid-printable .anvil-data-row-panel>.data-row-col {
border: 1px solid #888 !important;
}