@media screen and (min-width: 700px) {
  #edit-field-taxon-groups .form-type-checkbox {
    display: inline-block;
    width: 45%;
  }
}

@media screen and (min-width: 1100px) {
  #edit-field-taxon-groups .form-type-checkbox {
    display: inline-block;
    width: 31%;
  }
}