SOURCE

<div id="main">
  <div style="background-color:coral;"></div>
  <div style="background-color:lightblue;"></div>
  <div style="background-color:pink;"></div>
</div>

#main {
    width: 180px;
    height: 300px;
    border: 5px solid #c3c3c3;
    display: -webkit-flex;
    display: flex;
    -webkit-flex-wrap: wrap;
    flex-wrap: wrap;
    -webkit-align-content:center;
    align-content: center;
}

#main div {
    width: 160px;
    height: 70px;
}