html {
  background: url(../images/background-contractor-greyscale.jpg) no-repeat center center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}

div.logo {
  height: 20em;
  position: relative
}

div.logo img {
  margin: 0;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-right: -50%;
  transform: translate(-50%, -50%)
}