<script language="javascript">

 var d=new Date();

 var weekday=new Array("1","2","3","4","5","6","7");

 var curday=d.getMonth()+1+"."+d.getDate();

 var setday="1.28";//自定义的日期

 if(curday==setday){

  document.write('<link rel="stylesheet"  href="/skin/skyweb/css/sky.css"  type="text/css" />');

 }else{

  document.write('<link rel="stylesheet"  href="/skin/skyweb/css/skyred.css"  type="text/css" />');

 }

</script>

 思良：即1月28日就调用sky.css，其他时间调用skyred.css。测试能用（自己改了下），其他效果可以看原文。

下面的没测试。

原文：

<script language="javascript">
var d=new Date();
var weekday=new Array("1","2","3","4","5","6","7");
var curday=d.getMonth()+1+"."+d.getDate();
var setday="1.1";//自定义的日期
if(curday==setday){
document.write('<link rel="stylesheet" href="'+setday+'.css" type="text/css" />');
}else{
document.write('<link rel="stylesheet" href="'+weekday[d.getDay()]+'.css" type="text/css" />');
}
</script>

 按周：

<script language="javascript">
 var d=new Date();
 var weekday=new Array("1","2","3","4","5","6","7"); 
 document.write('<link rel="stylesheet"  href="'+weekday[d.getDay()]+'.css"  type="text/css" />');
</script>
或者：

<link rel="stylesheet" href="1.css" type="text/css" id="mycss"/>

<script type="text/javascript">
window.onload=function(){
var date=new Date();
var day=date.getDay();
var xing=new Array("1","2","3","4","5","6","7");

var cssDiv=document.getElementById("mycss");

switch(xing[day]) {
case "1":
cssDiv.href="1.css";
break;
case "1":
cssDiv.href="2.css";
break;
case "2":
cssDiv.href="1.css";
break;
case "3":
cssDiv.href="3.css";
break;
case "4":
cssDiv.href="4.css";
break;
case "5":
cssDiv.href="5.css";
break;
case "6":
cssDiv.href="6.css";
break;
case "7":
cssDiv.href="7.css";

}
}

</script>