SOURCE

<div class="box">
  <div class="th1"> </div>
    <div class="th2"> </div>
    <div class="th3"> </div>
</div>

.box{
  display:flex;
  justify-content:center;
  align-items:center;
  background-color:gray;
width:300px;
  height:300px;
}
.th1{
  display:inline-flex;
  background-color:black;
    width:200px;
  height:200px;
}