.layout--twocol {
  display: flex;
  flex-wrap: nowrap;
  justify-content: space-between;
}

.layout--twocol > .layout__region {
  flex: 0 1 100%;
}

@media screen and (min-width: 40em) {
  .layout--twocol > .layout__region--column {
    flex: 0 1 50%;
  }
}