<!doctype html>
<head>
<link rel="stylesheet" href="/slow-response">
<script>
const params = new URLSearchParams(window.location.search);
if (params.has('red')) {
document.documentElement.style.background = "red";
} else {
document.documentElement.style.background = "blue";
}
</script>
<style>
html {
margin: 0;
}
</style>
</head>
<body>
</body>