<div class="container">
  <div class="item">Vertical Centering with CSS</div>
</div>

.container {
  position: relative;
  display: table;
  height: 80vh;
  width: 80vw;
  border: 3px solid black;
  margin: auto;
  padding: 10px;
}

.item {
  display: table-cell;
  background: teal;
  color: #fffed3;
  font-size: 3rem;
  text-align: center;
  vertical-align: middle;
}