<div class='heading'><h1>We are inline-flex elements</h1></div>
<div class="container red">
  <div class="item inner green"></div>
  <div class="item inner green"></div>
  <div class="item inner green"></div>
  <div class="item inner green"></div>
  <div class="item inner green"></div>
  <div class="item inner green"></div>
</div>

<div class="container blue">
  <div class="item inner orangered"></div>
  <div class="item inner orangered"></div>
  <div class="item inner orangered"></div>
  <div class="item inner orangered"></div>
  <div class="item inner orangered"></div>
  <div class="item inner orangered"></div>
</div>

.container {
  display: inline-flex;
  flex-wrap: wrap;
  width: 40%;
  height: 300px;
  margin: 20px;
  padding: 10px;
}

.container.red {
  background-color: salmon;
}

.container.blue {
  background-color: lightblue;
}

.item {
  flex: 1 1 50px;
  height: 100px;
  margin: 10px 10px 0 0;
}

.item.green {
  background-color: green;
}

.item.orangered {
  background-color: orangered;
}

h1 {
  color: darkblue;
}

.heading {
  text-align: center;
}