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                        /導(dǎo)航條菜單的制作

為什么加了給 a標(biāo)簽加了左右的padding之后為什么寬度會(huì)不斷的增加

求解釋為什么加了給 a標(biāo)簽加了左右的padding之后為什么寬度會(huì)不斷的增加

<html?xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta?http-equiv="Content-Type"?content="text/html;?charset=utf-8"?/>
<title>導(dǎo)航菜單</title>
<style?type="text/css">
*{margin:0;?padding:0;?font-size:14px;}
a{color:#333;text-decoration:none?;padding:5px;}???//注意這里的padding
.nav{list-style:none;?height:30px;?border-bottom:10px?solid?#F60;?margin-top:20px;?padding-left:50px;}
.nav?li{float:left}
.nav?li?a{display:block;?height:30px;text-align:center;?line-height:30px;?width:80px;?background:#efefef;?margin-left:1px;}
.nav?li?a.on,?.nav?li?a:hover{background:#F60;color:#fff;?}
</style>

<script>
window.onload=function(){
	var?oNav=document.getElementsByTagName('ul')[0];
	var?aA=oNav.getElementsByTagName('a');
	for(var?i=0;?i<aA.length;?i++){
		aA[i].onmouseover=function(){
			if(this.className!="on"){
				clearInterval(this.time);
				var?This=this;
				This.time=setInterval(function(){
					This.style.width=This.offsetWidth+8+"px";
					if(This.offsetWidth>=120)
					clearInterval(This.time);
				},30)
			}
		}
		aA[i].onmouseout=function(){
			if(this.className!="on"){
				clearInterval(this.time);
				var?This=this;
				this.time=setInterval(function(){
					This.style.width=This.offsetWidth-8+"px";
					if(This.offsetWidth<=80){
						This.style.width='80px';
						clearInterval(This.time);
					}
				},30)
			}
		}
	}
}
</script>


</head>
<body>

<ul?class="nav">
????<li><a?class="on"?href="#">首　　頁(yè)</a></li>
????<li><a?href="#">關(guān)于我們</a></li>
????<li><a?href="#">產(chǎn)品展示</a></li>
????<li><a?href="#">售后服務(wù)</a></li>
????<li><a?href="#">聯(lián)系我們</a></li>
??</ul>

</body>
</html>