TOP /すぐに使えるJavaScript スタイルシートを切り替える
<head>
<link id="sheet"rel="stylesheet" type="text/css" href="001.css">
</head>
<body>
<script type="text/javascript"><!--
function changecss(css){
  document.getElementById("sheet").href = css;
}
//--></script>
<form>
<select name="select1">
<option value="001.css">blue</option>
<option value="002.css">magenta</option>
<option value="003.css">gray</option>
</select>
<input type="button" value="stylesheet" onClick="changecss(this.form.select1.value)">
</form>
</body>