得到css style

   //根据ID返回dom元素
 2     var $ = function(id){return document.getElementById(id);}
 3     //返回dom元素的当前某css值
 4     var getCss = function(obj,name){
 5         //ie
 6         if(obj.currentStyle) {
 7             return obj.currentStyle[name];
 8         }
 9         //ff
10         else {
11             var style = document.defaultView.getComputedStyle(obj,null);
12             return style[name];
13         }
14     }