#content
{
  background: url( "/images/unser_weg.jpg") no-repeat 100px center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}

body.dark_mode
{
  & #content
  {
    background-image: none;
  }
}