Edit in JSFiddle

<h2>
flex-grow
</h2>
<div class="wrapper default">
  <div class="box a">A</div>
  <div class="box b">B</div>
  <div class="box c">C</div>
  <div class="box d">D</div>
  <div class="box e">E</div>
  <div class="box f">F</div>
</div>

body {
  padding: 20px;
  font-family: Helvetica;
}

.wrapper {
  display: flex;
  background-color:#eee;
  margin-bottom:10px;
  border:1px solid #CCC;
  

}




.default {
  
}

.order1 {
  .a { order : 1;}
}

.box {
  background-color: #20262e;
  color: #fff;
  border-radius: 3px;
  padding: 20px;
  margin:10px;
  font-size: 14px;
  width:fit-content;
}