向当前style sheet中插入一个新的style实现方法

　　/**

　　* Add a stylesheet rule to the document (may be better practice, however,

　　* to dynamically change classes, so style information can be kept in

　　* genuine styesheets (and avoid adding extra elements to the DOM))

　　* Note that an array is needed for declarations and rules since ECMAScript does

　　* not afford a predictable object iteration order and since CSS is

　　* order-dependent (i.e., it is cascading); those without need of

　　* cascading rules could build a more accessor-friendly object-based API.

　　* @param {Array} decls Accepts an array of JSON-encoded declarations

　　* @example

　　addStylesheetRules([

　　['h2', // Also accepts a second argument as an array of arrays instead

　　['color', 'red'],

　　['background-color', 'green', true] // 'true' for !important rules

　　],

　　['.myClass',

　　['background-color', 'yellow']

　　]

　　]);

　　*/

　　function addStylesheetRules (decls) {

　　var style = document.createElement('style');

　　document.getElementsByTagName('head')[0].appendChild(style);

　　if (!window.createPopup) { /* For Safari */

　　style.appendChild(document.createTextNode(''));

　　}

　　var s = document.styleSheets[document.styleSheets.length - 1];

　　for (var i=0, dl = decls.length; i < dl; i++) {

　　var j = 1, decl = decls[i], selector = decl[0], rulesStr = '';

　　if (Object.prototype.toString.call(decl[1][0]) === '[object Array]') {

　　decl = decl[1];

　　j = 0;

　　}

　　for (var rl=decl.length; j < rl; j++) {

　　var rule = decl[j];

　　rulesStr += rule[0] + ':' + rule[1] + (rule[2] ? ' !important' : '') + ';\n';

　　}

　　if (s.insertRule) {

　　s.insertRule(selector + '{' + rulesStr + '}', s.cssRules.length);

　　}

　　else { /* IE */

　　s.addRule(selector, rulesStr, -1);

　　}

　　}

　　}

　　addStylesheetRules(["div.content", ["color": "#000"], ["border-width","1px"], ["border-style", "solid"]])

　　<style>

　　div.content{color:#000;border:1px solid}

　　</style

　　addStylesheetRules(

　　[selector, [attr, value], …],

　　[selector, [attr, value], …]

　　);