404.html

<!doctype html>
<html lang=en >
<head>
<meta charset=utf-8 >
<meta name=author content='Theo Armour' >
<title></title>
</head>
<body>
<script>
// Welcome. Anybody who looks at the source code of other people's error pages must be wonderful!

// Written in 'everything-JavaScript' style

	document.body.style.cssText = ' font: bold 12pt monospace; height: ' + window.innerHeight + 'px; overflow: hidden;';

	const user = 'ladybug-tools';
	const repo = '/spider';
	const info = document.body.appendChild( document.createElement( 'div' ) );

	document.title = '404 for ' + user + repo
	info.innerHTML =

	'<div style=background-color:white;left:0;margin:auto;max-width:50%;opacity:0.5;right:0;text-align:center; >' +
		'<h1 title="This is the 404 error page" >Oops</h1>' +
		'<h2>Website: <a href=https://' + user + '.github.io' + repo + ' title="Go to the apps" >' + user + '.github.io' + repo + '</a></h2>' +
		'<h2>Source code: <a href=https://github.com/' + user + repo + ' title="Go to the source code" >github.com/' + user + repo + '</a></h2>' +
	'</div>';

	toggleBackgroundGradient();


	function toggleBackgroundGradient() {

// 2016-07-18

		var col = function() { return ( 0.5 + 0.5 * Math.random() ).toString( 16 ).slice( 2, 8 ); };
		var pt = function() { return ( Math.random() * window.innerWidth ).toFixed( 0 ); }
		var image = document.body.style.backgroundImage;

		document.body.style.backgroundImage = image ? '' : 'radial-gradient( circle farthest-corner at ' +
			pt() + 'px ' + pt() + 'px, #' + col() + ' 0%, #' + col() + ' 50%, #' + col() + ' 100% ) ';

	}

</script>
</body>
</html>