<div class="grid-container">
  <div class="grid-item gi-1">1</div>
  <div class="grid-item gi-2">2</div>
  <div class="grid-item gi-3">3</div>
  <div class="grid-item gi-4">4</div>
</div>

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  padding: 2%;
}

.grid-container {
  width: 310px;
  height: 310px;
  border: 5px solid #212226;
  display: grid;
  grid-template-rows: repeat(3, 1fr);
  grid-template-columns: repeat(3, 1fr);
  grid-auto-flow: column;
}

.grid-item {
  font-size: 2rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #71D99E;
  background-color: #3A8C7D;
}