JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="flex-container">
  <li class="flex-item">1 and 2 <br> and more</li>
  <li class="flex-item">2</li>
  <li class="flex-item">3</li>
  <li class="flex-item">4</li>
  <li class="flex-item">5</li>
  <li class="flex-item">6</li>
</ul>

CSS

.flex-container {
  padding: 0;
  margin: 0;
  list-style: none;
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-flex-flow: row wrap;
}

.flex-item {
  background: tomato;
  width: 23%;
  margin: 10px 1% 0 1%;
  float: left;
  line-height: 150px;
  color: white;
  font-weight: bold;
  font-size: 3em;
  text-align: center;
}

@media (max-width: 640px){
  .flex-item {
    width: 33%;
  }
}