flex-wrap

HTML

<div class="container">
  <div class="item item-1">1</div>
  <div class="item item-2">2</div>
  <div class="item item-3">3</div>
</div>

SCSS

.container {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  width: 400px;
}


.item {
  border: 1px solid #ED9999;
  padding: 14px;
}

.item-1 {
  
}

.item-2 {
  
}

.item-3 {
  
}