<div class="grid">
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>

.grid {
  display: grid;
  grid-template-columns: repeat(4, 100px);
  grid-template-rows: repeat(2,100px);
  grid-gap: 1px;
  background-color: #000;
  width: 403px;
  height: 201px;
  border:1px solid #000;
  margin: 10px auto;
}

.grid > div {
  background-color: #fff;
}

.grid::after {
  content: " ";
  background-color: red;
  grid-column: 2 / 4;
  grid-row: 1 / 3;
}