var newcss = document.createElement('link');
newcss.rel = 'stylesheet';
newcss.type = 'text/css';
if (screen.width <= 1440) {
  newcss.href = "/style/piano-small.css";
} else {
  newcss.href = "/style/piano.css";
}
document.getElementsByTagName('head')[0].appendChild(newcss);