Help with btn-group in Bootstrap 4

I'm working with Bootstrap 4 I have the following code:

<?php $aprobar = '<form autocomplete="off" class="was-validated" method="post" action= "pedidos.php?id='.$rowid.'&user='.$rowUser.'"><button type="submit" class="btn btn-success  btn-sm" name="aprobar_pago_pedido_btn">Aprobar  <i class="fa fa-check-circle"></i></button> </form>';

      $rechazar = '<form autocomplete="off" class="was-validated" method="post" action= "rechazar.php?id='.$rowid.'&user='.$rowUser.'&asunto=pedido"><button type="submit" class="btn btn-danger btn-sm  btn-block" name="rechazar_pago_pedido_btn">Rechazar  <i class="fa fa-times-circle"></i></button> </form>';

      $link = '<div class="btn-group-vertical" role="group" >'. $aprobar . $rechazar . '</div>';

Just as the code is functional but aesthetically the buttons are not the same size, I would like to know how I can make the buttons 100% of the width of the cell where they are printed

<td>'.$link .'</td>