如何更改input file 的按钮？_html/css_WEB-ITnose

<style type="text/css">.button{width:100px;height:30px;}.fileupload{filter:Alpha(opacity=0);opacity:0;position:absolute;z-index:1}</style><input id="fileupload" class="button fileupload" type="file" /><div style="position:absolute;top:40px;left:100px;background:green;height:100px;width:300px">	<button id="btnUpload" type="button" class="button">点我试试看</button></div><script type="text/javascript">	function offset(ele){		if(!ele || ele.nodeType != 1){			return null;		}		if(!ele.parentNode){			return {top:ele.offsetTop,left:ele.offsetLeft};		}		var os = offset(ele.parentNode) || {};		return {top:ele.offsetTop + os.top || 0,left:ele.offsetLeft + os.left || 0};	}	var fileuploader = document.getElementById("fileupload"),	    btnUploader = document.getElementById("btnUpload");	var o = offset(btnUploader);	fileuploader.style.top=o.top+"px";	fileuploader.style.left=o.left+"px";</script>