<div class="container">
  <div class="box green">
    Box ⚡️
  </div>
  <div class="box blue">
    Box ⚡️⚡️
  </div>
</div>
<div class="container col">
  <div class="box green">
    Box ⚡️
  </div>
  <div class="box blue">
    Box ⚡️⚡️
  </div>
</div>

* {
  margin: 0;
  padding: 0;
  font-family: Roboto,"Helvetica Neue",Arial,sans-serif;
}

.container {
    width: 100vw;
    height: 100vh;
    display: flex;
    flex-direction: row; /* horizontal main axis */
    justify-content: center;
    align-items: center;
}
.container.col {
    flex-direction: column; /* vertical main axis */
}
.box {
    color: #fff;
    width: 300px;
    margin: 10px;
    padding: 10px;
    text-align: center;
}
.green {
    background: green;
}
.blue {
    background: blue;
}