body {
  background: #000000 url('../img/koala.jpg') no-repeat center center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  background-size: cover;
  -o-background-size: cover;
}

.overlay {
	display:none;
	position:fixed;
	overflow:auto;
	z-index:99;
  height: 100%;
  width: 100%;
  position: fixed; /* Stay in place */
  z-index: 1; /* Sit on top */
  left: 0;
  top: 0;
  background-color: rgb(0,0,0); /* Black fallback color */
  background-color: rgba(0,0,0, 0.7); /* Black w/opacity */
  overflow-x: hidden; /* Disable horizontal scroll */
  transition: 0.5s;
  }