.product .field--name-variations .form-actions {
  bottom: 3rem;
  left: 1rem;
  margin: 0 0 1.25rem;
  max-width: calc(100% - 2rem);
  position: fixed;
  width: 100%;
  z-index: 99;
}

@media screen and (min-width: 991px) {
  .product .field--name-variations .form-actions {
    bottom: auto;
    left: auto;
    max-width: 100%;
    position: relative;
  }
}