body {
    background: url("https://source.unsplash.com/DbwYNr8RPbg/1920x1080") no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
  }
#content {
    
    position: relative; 
}

html {
    scroll-padding-top: 70px; /* height of sticky header */
  }