<div class="aaa">
  <div class="bbb">1</div>
  <div class="bbb">2</div>
  <div class="bbb">3</div>
  <div class="bbb">4</div>
  <div class="bbb">5</div>
  <div class="bbb">6</div>
  <div class="bbb">7</div>
  <div class="bbb">8</div>
  <div class="bbb">9</div>
  <div class="bbb">10</div>
  <div class="bbb">11</div>
</div>

.aaa {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  justify-content: flex-start;
  align-items: stretch;
  align-content: flex-start;
  /*height: 100px;*/ }

.bbb {
  width: 50px;
  height: 50px;
  background-color: green;
  margin: 2px; }