css grid how to make last item full width

https://stackoverflow.com/questions/54370822/how-to-make-the-items-in-the-last-row-consume-remaining-space-in-css-grid

.grid {
    display: grid;
    grid-template-columns: auto auto auto;
    justify-items: start;
    grid-gap: 10px;
}

.grid div {
  border: 1px solid #ccc;
  width: 100%;
}

.grid > *:nth-child(3n-1) {
  justify-self: center;
  text-align: center;
}

.grid > *:nth-child(3n) {
  justify-self: end;
  text-align: right;
}

.grid > *:nth-child(3n-1):nth-last-of-type(1) {
  border-color: red;
  grid-column: span 2;
}

.grid > *:nth-child(3n-2):nth-last-of-type(1) {
  border-color: red;
  grid-column: span 3; 

}