http://cdpn.io/LGova

codice:
<div>
  <p>
    lorem ipsum
  </p>
  
  <section>
    100% full width
  </section>
  
</div>
CSS

codice:
div { width: 70%; margin: 0 auto; background: #2f85ad; height: 100vh;}

section {
  height: 50px;
  width: 100%;
  position: absolute;
  left: 0;
  background: #93b07f;
}