<div class="content">
  <div class="flex-layout">
    <div class="header">
      <h1>Heading Heading</h1>
      <a href="">Link Link Link</a>
    </div>
    <button class="btn">Button</button>
  </div>
</div>
html {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
*,
*:before,
*:after {
  box-sizing: inherit;
}
body {
  background: lightgrey;
}
.content {
  background: white;
  padding: 10px;
  max-width: 900px;
  margin:auto;
  box-sizing: border-box;
}
.flex-layout {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.flex-layout h1{margin:0;padding:1em 0}
@media (max-width: 700px) {
  .btn {
    margin-top: auto;
  }
}
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