function setBodyStyle()
{
  var cWidth    = document.documentElement.clientWidth;
  var bodyClass = '';
  if ( cWidth < 800 ) bodyClass += 'small';
  if ( cWidth < 480 ) bodyClass += ' smaller';
  document.body.className = bodyClass;
}

window.onload   = setBodyStyle;
window.onresize = setBodyStyle;