.grid-container-18 {
  display: grid;
  grid-template-columns: 3fr 2fr;
  grid-template-rows: 2fr 2fr;
  column-gap: 10px;
  row-gap: 10px;
  grid-template-areas: 
    "a b"
    "a c"
  ;
}

.a-18 {
  grid-area: a;
}
.b-18 {
  grid-area: b;
}
.c-18 {
  grid-area: c;
}

@media screen and (max-width: 767px) {
  .grid-container-18 {
    grid-template-columns: 1fr;
    grid-template-rows: repeat(3, auto);
    grid-template-areas:
      "a"
      "b"
      "c"
    ;

  } 
  
}