grid-layout-1.css

* {
  box-sizing: border-box;
}

.layout {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
}
.child {
  min-height: 100px;
  background: orange;
  text-align: center;
  line-height: 100px;
  border: 5px solid white;
}

.child:last-of-type {
  grid-column: 1 / -1;
}