Untitled

<!DOCTYPE html>
<html>
<head>
<style>
@media only screen and (max-width: 768px) {
    .flex-container {
        display: column;
    }

}
.flex-container {
  display: flex;
  background-color: DodgerBlue;
}

.flex-container > div {
  background-color: #f1f1f1;
  width: 100px;
  margin: 10px;
  text-align: center;
  line-height: 75px;
  font-size: 30px;
}
</style>
</head>
<body>


<div class="flex-container">
  <div>1</div>
  <div>2</div>

</div>

</body>
</html>