<div class="game-board">
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
  <div class="box">1fr x 1fr</div>
</div>

.game-board {
    display: grid;
    grid-template-rows: 1fr 1fr 1fr;
    grid-template-columns: 1fr 1fr 1fr;
}

// for some css stylings
.box {
  background: #444;
  border: 1px solid #555;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #AAA;
}