请问如何改变网页背景颜色

问题遇到的现象和发生背景

问题：如果让文件“换皮肤的页面.html"能够实现页面换皮肤功能？
已经有

img

img

问题相关代码，请勿粘贴截图
<HTML>
<HEAD>

<META http-equiv="Content-Type" content="text/html; charset=gb2312">

</HEAD>

<TITLE>改变页面风格</TITLE>
<LINK id="1" type="text/css" rel="stylesheet" href="style/mr.css" >
</HEAD>
<BODY leftmargin="0" topmargin="0" marginwidth="0" marginheight="0">
<TABLE width="90%" border="0" cellspacing="0" cellpadding="0" align="center">
<TR>
<TD>选择界面风格：<SELECT onChange="document.styleSheets[0].href=this.options[this.selectedIndex].value+'.css'" >
<OPTION value="Style/mr1" >默认风格</OPTION>
<OPTION value="Style/red"selected >粉红风情</OPTION>
<OPTION value="Style/blue1">蓝色天空</OPTION>
<OPTION value="Style/block1">灰暗忧郁</OPTION>
<OPTION value="Style/green"> 绿色地带</OPTION>
<OPTION value="Style/blue"> 蓝色港湾</OPTION>
<OPTION value="Style/block"> 黑白相间</OPTION>
</SELECT></TD>
</TR>
</TABLE>
</BODY>
</HTML>
运行结果及报错内容
我的解答思路和尝试过的方法
我想要达到的结果

<HTML>
  <HEAD>
   
  <META http-equiv="Content-Type" content="text/html; charset=gb2312">
   
  </HEAD>
   
  <TITLE>改变页面风格</TITLE>
  <LINK id="1" type="text/css" rel="stylesheet" href="style/mr.css" >
  </HEAD>
  <BODY leftmargin="0" topmargin="0" marginwidth="0" marginheight="0">
  <TABLE width="90%" border="0" cellspacing="0" cellpadding="0" align="center">
  <TR>
  <TD>选择界面风格：<SELECT id="select" onchange="change()" >
  <OPTION value="Style/mr" >默认风格</OPTION>
  <OPTION value="Style/red"selected >粉红风情</OPTION>
  <OPTION value="Style/blue1">蓝色天空</OPTION>
  <OPTION value="Style/block1">灰暗忧郁</OPTION>
  <OPTION value="Style/green"> 绿色地带</OPTION>
  <OPTION value="Style/blue"> 蓝色港湾</OPTION>
  <OPTION value="Style/block"> 黑白相间</OPTION>
  </SELECT></TD>
  </TR>
  </TABLE>
  <script>
    function change(val) {
      var val = document.getElementById('select').value
      dynamiccss(val+'.css')
    }
    
    function dynamiccss(path){
      if(!path || path.length === 0){
      throw new Error('argument "path" is required !');
      }
      var head = document.getElementsByTagName('head')[0];
      var link = document.createElement('link');
      link.href = path;
      link.rel = 'stylesheet';
      link.type = 'text/css';
      head.appendChild(link);
    }


  </script>
  </BODY>
  </HTML>