@media screen and (max-width: 650px) {
  div.ScreenHorizontal {
    display: none;
  }
}

@media screen and (min-width: 651px) {
  #leftside {width: 50%; float: left;}
  #rightside {width: 50%; float: left;}
  div.ScreenVertical {
    display: none;
  }
}