<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
</div>
<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>
<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>
<div class="parent">
  <div class="child"></div>
  <div class="child wide">wide</div>
  <div class="child"></div>
</div>
<div class="parent">
  <div class="child wide">wide</div>
  <div class="child"></div>
  <div class="child"></div>
</div>
<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child wide">wide</div>
  <div class="child"></div>
</div>
* {
  margin: 0;
  padding: 0;
}
body {
  display: block;
  min-width: 600px;
  max-width: 1000px;
  margin: 2em auto;
  padding: 0 20px;
}



.parent {
  display: flex;
  flex-wrap: nowrap;
  margin: 0 calc(20px / 2 * -1);
}
.parent + .parent {
  margin-top: 20px;
}
.child {
  flex: 1;
  height: 40px;
  margin: 0 calc(20px / 2);
  background: #3498db;
  color: #fff;
  font-size: 1.2rem;
  text-align: center;
  line-height: 40px;
}
.wide {
  flex: 2;
}

External CSS

  1. https://fonts.googleapis.com/css?family=Open+Sans:400,300

External JavaScript

This Pen doesn't use any external JavaScript resources.