.layout--troiscol {
  --gap: 40px;
  display: flex;
   flex-wrap: wrap;
   gap: var(--gap);
}

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

@media screen and (min-width: 980px) {
  .layout--troiscol > .layout__region--column {
    flex: 0 1 calc(33% - var(--gap));
  }
}