<div class="content">
  <h1>heading 1</h1>
  <h2>heading 2</h2>
  <p>Some more or less text</p>
  <a href="/" class="button">Click me</a>
</div>

-------------------
|heading 1          |
|heading 2          |
|paragraph text     |
|can have many      |
|rows               |
|                   |
|                   |
|                   |
|link-button        |
 -------------------

.container {
  display: flex;
}

.button {
  align-self: flex-end;
}

.content {
    height: 400px;
    background: #000;
    color: #fff;
}
.button {
    transform: translateY(-100%);
    display: inline-block;
}

.content{
  display: flex;
  justify-content: space-between;
  flex-direction: column;
}

<div class="content">
  <div>
    <h1>heading 1</h1>
    <h2>heading 2</h2>
    <p>Some more or less text</p>
  </div>

  <div>
    <a href="/" class="button">Click me</a>
  </div>
</div>

-------------------
|heading 1          |
|heading 2          |
|paragraph text     |
|can have many      |
|rows               |
|                   |
|                   |
|                   |
|link-button        |
 -------------------

.content{
  display: flex;
  flex-direction: column;
}
.content a{
  position: fixed;
  bottom: 0;
}