var nod = document.createElement(“style”),   str = “body{background:#000;color:#fff} a{color:#fff;text-decoration:none;} a:hover{color:red;text-decoration:underline}”;  nod.type=”text/css”;  if(nod.styleSheet){         //ie下  nod.styleSheet.cssText = str;  } else {  nod.innerHTML = str;       //或者写成 nod.appendChild(document.createTextNode(str))  }  document.getElementsByTagName(“head”)[0].appendChild(nod);