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

.item {
  background: blue;
  box-sizing: border-box;
  border: 2px solid blue;
  border-radius: 8px;
}

.item:hover {
  border: 2px solid #000;
}

.grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  width: 50vw;
  height: 50vh;
  grid-gap: 30px;
  margin: 30px auto;
}