From the source of the error page:
if we get here, that means even the offline pages on sstatic are offline
What you saw was a an outage that included the http://sstatic.net offline pages, wide enough for the pretty offline pages to not be available either. The fugly banner message is the backup to the backup.
It was a very brief outage, and it was planned. We can all remove the tin-foil hats and move along.
For reference, the full source of the error page is:
<html>
<head>
<title>We are Offline</title>
<style type="text/css">
body { margin: 0; padding: 0; }
iframe { border: 0; }
</style>
</head>
<body>
<iframe width="100%" height="100%" id="pageFrame"></iframe>
<script type="text/javascript">
setTimeout(function () { location.reload(true); }, 300000);
var hostName = window.location.hostname;
var directory = '';
</script>
<script type="text/javascript" src="http://sstatic.net/error-director.js"></script>
<script type="text/javascript">
if (top == self && directory) {
document.getElementById('pageFrame').src = 'http://sstatic.net/' + directory + '/app_offline.htm';
} else {
// if we get here, that means even the offline pages on sstatic are offline
document.getElementById('pageFrame').style.height = "0px";
document.write("<h2>Stack Exchange is currently offline, we'll be back shortly!<\/h2>");
}
</script>
</body>
</html>
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