.spacer { display:block; clear:both; }
.height-small   { height:20px; }
.height-medium  { height:40px; }
.height-large   { height:80px; }
.height-x-large { height:140px; }

  @media (max-width: 768px) { 
    .height-small   { height:15px; }
    .height-medium  { height:30px; }
    .height-large   { height:60px; }
    .height-x-large { height:110px; }
  }
  @media (max-width: 480px) { 
    .height-small   { height:10px; }
    .height-medium  { height:20px; }
    .height-large   { height:40px; }
    .height-x-large { height:70px; }
  }