Viewport not working

by Rahul Khan

HTML

<body>
  <div class="nav"></div><!-- Nav --> 
</body>

CSS

body {
  line-height: 1; 
  width: 100%;
  font-family: 'Droid Sans', sans-serif;
  margin: 0 auto; 
}

.nav {
  margin: 0 auto; 
  border-top: 6px solid #9FCC7F; 
  width: 100vw;
}