@media screen and (max-width: 767px) {
  .header {
    display: table;
    position: relative;
    width: 100%;
    height: 100%;
    background: url(../img/bg.jpg) no-repeat center center scroll;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
  }
}

@media screen and (min-width: 768) and (max-width: 1024px) {
  .header {
    display: table;
    position: relative;
    width: 100%;
    height: 100%;
    background: url(../img/bg.jpg) no-repeat center center scroll;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
  }
}