#printarea {
position: relative;
margin: 0 auto;
width: 400px;
}
   body,html
    {
   width:400px;
   margin: 0 auto;
   }

@page {
  size: 91.44mm 53.34; // set appropriately
  margin: 0;
}
@media print {
  html, body {
    width: 91.44mm; // set appropriately
    height: 53.34mm; // set appropriately
  }
  /* ... the rest of the rules ... */
}