.carousel {
  z-index: -99;
}

/* keeps this behind all content */
.carousel-item {
  background-size: cover;
  -moz-background-size: cover;

  position: fixed;
  width: 100%;
  height: 100%;
  -webkit-transition: opacity 1s;
  -moz-transition: opacity 1s;
  -ms-transition: opacity 1s;
  -o-transition: opacity 1s;
  transition: opacity 1s;
}