Persistent stylesheet switcher

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"https://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>style changer button</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link id="mystyle" rel="stylesheet" type="text/css" href="style1.css">

window.onload=function() {
obj0=document.getElementById('mybutton');
obj1=document.getElementById('mystyle');
readCookie();
obj0.onclick=function() {
stylech();
}
}

function setCookie() {
exp=new Date();
plusMonth=exp.getTime()+(31*24*60*60*1000);
exp.setTime(plusMonth);
document.cookie='style='+styleid+';expires='+exp.toGMTString();
}

</script>

</head>
<body>

<ul>
<li><a href="anotherPage.html">another page</a></li>
</ul>

</body>
</html>