获取元素的真正样式

   function getRealStyle(id,styleName) {       var element = document.getElementById(id);       var realStyle = null;        if(element.currentStyle) {           realStyle = element.currentStyle[styleName];       }else if(window.getComputedStyle) {           realStyle = window.getComputedStyle(element, null)[styleName];       }       return realStyle;   }