<div class="container">
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

.container {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  justify-items: center;
  align-items:center;
  height: 90vh;
  width: 90vw;
  border: 3px solid black;
  margin: auto;
}

.item {
  width: 10vw;
  padding: 50px;
  background: teal;
}