Create div element relative to img width

index.html

<div class="wrapper">
  <div class="img-bloc">
    <img src="/"/>
    <div class="actions-bloc">
      <a href="#" class="btn">Learn more</a>
    </div>
  </div>
</div>

style.css

.wrapper {
  position: relative;
  display: inline-block;
}

.img-bloc {
  float:left;
}

.actions-bloc {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
}