Comment by ramzis

To center everything I added:

  .col-md-9 {
      width: 100%;
      margin-top: 1em;
  }

  .col-md-3 {
      width: 100% !important;
      margin-bottom: 1em;
  }

  .flex-md-row {
      flex-direction: column!important;
  }

  .flex-md-row {
      flex-direction: column-reverse!important;
  }

  .BorderGrid--spacious .BorderGrid-cell {
      padding-top: .2em;
      padding-bottom: .2em;
  }

  div.BorderGrid.BorderGrid--spacious > div:not(:first-child) {
      display: none;
  }