Type – Border

'formBorder' => [
  'label' => __( 'Border' ),
  'type' => 'ct-border',
],

Value Format

'formBorder' => [
  'width' => 1,
  'style' => 'solid',
  'color' => [ 'color' => 'var(--main)' ],
],

style - Can be solid, dashed, dotted, or none.