添加移除外部的css样式

//前台调用
var $ = function (_this) {
	return new Base(_this);
}

//基础库
function Base(_this) {
	//创建一个数组，来保存获取的节点和节点数组
	this.elements = [];
	if (_this != undefined) {    //_this是一个对象，undefined也是一个对象，区别与typeof返回的带单引号的'undefined'
		this.elements[0] = _this;
	}
}

//添加link或style的CSS规则
Base.prototype.addRule = function (num, selectorText, cssText, position) {
	var sheet = document.styleSheets[num];
	if (typeof sheet.insertRule != 'undefined') {//W3C
		sheet.insertRule(selectorText + '{' + cssText + '}', position);
	} else if (typeof sheet.addRule != 'undefined') {//IE
		sheet.addRule(selectorText, cssText, position);
	}
	return this;
}

//移除link或style的CSS规则
Base.prototype.removeRule = function (num, index) {
	var sheet = document.styleSheets[num];
	if (typeof sheet.deleteRule != 'undefined') {//W3C
		sheet.deleteRule(index);
	} else if (typeof sheet.removeRule != 'undefined') {//IE
		sheet.removeRule(index);
	}
	return this;
}