JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css">
<script src="https://fonts.googleapis.com/css?family=Open+Sans:400,300,300italic,400italic,600,600italic,700,700italic,800,800italic"></script>
<body>

  <div class="layout_wrapper">

    <div class="layout_container__content">
      <div class="content">
        <header class="content__header">
        
          <div class="breadcrumb">
            <span class="breadcrumb__text  breadcrumb__text--first">From </span><a class="breadcrumb__link" href="#">Dashboard</a><span class="breadcrumb__text"> to </span><a class="breadcrumb__link" href="#">Find records</a><span class="breadcrumb__text"> to </span>
            <h1 class="breadcrumb__current">Kylo Ren’s Command Shuttle™</h1>
          </div>
          
          <ul class="page_tools">
            <li class="page_tools__item">
              <button type="button" class="button  button--primary">Save</button>
            </li>
            <li class="page_tools__item">
              <button type="button" class="button">Cancel</button>
            </li>
          </ul>
          
        </header>
        
      </div>
    </div>

    <div class="layout_container__sidebar">
    
      <div class="sidebar">
        <article class="widget">
          <h2 class="widget__title">Widget</h2>
        </article>
      </div>
      
    </div>

  </div>
</body>

CSS

/* Removing this makes it work */
.breadcrumb__text::after {
  font-family: "FontAwesome";
  font-weight: 400;
}

/* Don't remove anything below */
.breadcrumb__text--first {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

* {
    box-sizing: inherit;
}

html {
    box-sizing: border-box;
}

html, body {
    padding: 0;
    margin: 0;
}

body {
  display: flex;
  flex-flow: column nowrap;
  align-items: stretch;
}

.layout_wrapper {
  flex: 1 1 auto;
  display: flex;
  flex-flow: row nowrap;
  align-items: stretch;
}

.layout_container__content {
  flex: 0 0 75vw;
}

.layout_container__sidebar {
  flex: 0 0 25vw;
}

.content {
  display: flex;
  flex-flow: row wrap;
  justify-content: space-between;
  align-items: stretch;
}

.content__header {
  outline: 1px solid blue;
  background-color: #434649;
  color: #ffffff;
  flex: 0 0 100%;
  display: flex;
  flex-flow: row nowrap;
}

.breadcrumb {
  outline: 3px dashed purple;
  flex: 1 1 auto;
  display: flex;
  flex-flow: row wrap;
  justify-content: flex-start;
}

.breadcrumb__text {
  flex: 0 0 2em;
  overflow: hidden;
  text-indent: -9999px; /* changed from 100% */
  white-space: nowrap;
  position: relative;
  text-align: center;
}

.breadcrumb__text::after {
  content: '\f105';
  padding: 0;
  text-indent: 0;
  position: absolute;
  top: 0;
  right: 0;
  width: 100%;
}

.breadcrumb__text--first {
  flex: 0 0 0;
}

.breadcrumb__text--first::after {
  content: none;
}

.breadcrumb__link {
  flex: 0 0 auto;
  display: inline-block;
  font-size: 0.8571rem;
}

.breadcrumb__current {
  flex: 0 0 100%;
  margin: 0;
}

.page_tools {
  outline: 3px dashed red;
  flex: 0 0 auto;
  display: flex;
  flex-flow: row nowrap;
  list-style: none outside none;
}