.grid-container-16 {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  grid-template-rows: auto auto;
  column-gap: 10px;
  row-gap: 10px;
  grid-template-areas: 
    "a1 a2 a3"
    "b b b"
  ;
}

.a1-16 {
  grid-area: a1;
}
.a2-16 {
  grid-area: a2;
}
.a3-16 {
  grid-area: a3;
}
.b-16 {
  grid-area: b;
}


@media screen and (max-width: 767px) {
  .grid-container-16 {
    grid-template-columns: 1fr;
    grid-template-rows: repeat(4, auto);
    grid-template-areas:
      "a1"
      "a2"
      "a3"
      "b"
    ;

  } 

}