JSFiddle - React, Tailwind, and code Playground

HTML

<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>
<div class="child-filler"></div>

CSS

* {
  box-sizing: border-box;
}
body {
    display: flex;
    flex-wrap: wrap;
}
.child {
    height: 50px;
    margin: 10px;
    flex: 1 1 50px;
    background-color: red;
    border: 1px solid black;
}
.child-filler {
  margin: 0 10px;
  flex: 1 1 50px;
  height: 0;
  border: 1px solid blue;
}