if (screen.width <= 1024) {
document.write('<link rel="stylesheet" type="text/css" href="sistema.css" />');
document.write('<style type="text/css"  media ="screen">@import url(sistema.css);</style>');
}
    if (screen.width >= 1280) {
document.write('<link rel="stylesheet" type="text/css" href="sistemax1280.css" />');
document.write('<style type="text/css"  media ="screen">@import url(sistemax1280.css);</style>');
}