在页面上添加样式标签

var style = document.createElement(\"style\"),
style.innerHTML = \".firstChildTest div:first-child {width: 2px;}\";

 style.append(document.createTextNode(\".firstChildTest div:first-child {width: 2px;}\"));

function copy_style(style_text) {    
    var tmp_div = document.createElement(\'div\');
    tmp_div.innerHTML = \'<p>x</p><style type=\"text/css\">\' + style_text + \'</style>\';

    return tmp_div.getElementsByTagName(\'style\')[0];
}

function addStyle(str){
    var el= document.createElement(\'style\');
    if(el.styleSheet) el.styleSheet.cssText= str;
    else{
        el.appendChild(document.createTextNode(str));
    }
    return document.getElementsByTagName(\'head\')[0].appendChild(el);
}