冬天，就要有冬天的404

前些天发现了一个巨牛的人工智能学习网站，通俗易懂，风趣幽默，忍不住分享一下给大家。点击跳转到网站。
先看效果：

源码：
pug代码部分:

.content
	canvas.snow#snow
	.main-text
		h1 Aw jeez.
			br
			| That page has gone missing.
		a.home-link(href='#') Hitch a ride back home.
	.ground
		.mound 
			.mound_text 404
			.mound_spade

scss部分：

$col-sky-top: #bbcfe1;
$col-sky-bottom: #e8f2f6;
$col-fg: #5d7399;
$col-blood: #dd4040;
$col-ground: #f6f9fa;

@mixin trees($direction, $size) {
	$shadow: ();
	
	@for $i from 1 through 16 {
		$space: $size * 1.2;
		$rand:  (random(20)/10 - 1) * 50px;
		$shadow: append($shadow, ($direction * $i * $space + $rand) (($direction * -$i * $space) + $rand) 15px lighten($col-fg, random(20) + 10%), comma);
	}
		
	box-shadow: $shadow;
}

html,
body {
	height: 100%;
	min-height: 450px;
	
	font-family: 'Dosis', sans-serif;
	font-size: 32px;
	font-weight: 500;
	color: $col-fg;
}

.content {
	height: 100%;
	position: relative;
	
	z-index: 1;
	background-color: mix($col-sky-top, $col-sky-bottom);
	background-image: linear-gradient(to bottom, $col-sky-top 0%, $col-sky-bottom 80%);
	overflow: hidden;
}

.snow {
	position: absolute;
	top: 0;
	left: 0;
	pointer-events: none;
	z-index: 20;
}

.main-text {
	padding: 20vh 20px 0 20px;
	
	text-align: center;
	line-height: 2em;
	font-size: 5vh;
}

.home-link {
	font-size: 0.6em;
	font-weight: 400;
	color: inherit;
	text-decoration: none;
	
	opacity: 0.6;
	border-bottom: 1px dashed transparentize($col-fg, 0.5);
	
	&:hover {
		opacity: 1;
	}
}

.ground {
	height: 160px;
	width: 100%;
	position: absolute;
	bottom: 0;
	left: 0;
	
	background: $col-ground;
	box-shadow: 0 0 10px 10px $col-ground;
	
	$treeSize: 250px;
	&:before,
	&:after {
		
		// Trees
		content: '';
		display: block;
		width: $treeSize;
		height: $treeSize;
		position: absolute;
		top: -$treeSize/4;
		
		z-index: -1;
		background: transparent;
		transform: scaleX(0.2) rotate(45deg);
	}
	
	&:after {
		left: 50%;
		margin-left: -$treeSize / 1.5;
		@include trees(-1, $treeSize);
	}
	
	&:before {
		right: 50%;
		margin-right: -$treeSize / 1.5;
		@include trees(1, $treeSize);
	}
}

.mound {
	margin-top: -80px;
	
	font-weight: 800;
	font-size: 180px;
	text-align: center;
	color: $col-blood;
	pointer-events: none;
	
	$from-top: 50px;
	
	&:before {
		$w: 600px;
		$h: 200px;
		
		content: '';
		display: block;
		width: $w;
		height: $h;
		position: absolute;
		left: 50%;
		margin-left: -$w/2;
		top: $from-top;
		z-index: 1;
		
		border-radius: 100%;
		background-color: $col-sky-bottom;
		background-image: linear-gradient(to bottom, lighten($col-sky-top, 10%), $col-ground 60px);
	}
	
	&:after {
		// Blood
		$w: 28px;
		$h: 6px;
		content: '';
		display: block;
		width: $w;
		height: $h;
		position: absolute;
		left: 50%;
		margin-left: - 150px;
		top: $from-top + 18px;
		
		z-index: 2;
		background: $col-blood;
		border-radius: 100%;
		transform: rotate(-15deg);
		box-shadow: -($w * 2) ($h * 2) 0 1px $col-blood, -($w * 4.5) ($h) 0 2px $col-blood, -($w * 7) ($h * 4) 0 3px $col-blood,
	}
}

.mound_text {
	transform: rotate(6deg);
}

.mound_spade {
	$handle-height: 30px;
	
	display: block;
	width: 35px;
	height: 30px;
	position: absolute;
	right: 50%;
	top: 42%;
	margin-right: -250px;
	
	z-index: 0;
	transform: rotate(35deg);
	background: $col-blood;
	
	&:before,
	&:after {
		content: '';
		display: block;
		position: absolute;
	}
	
	&:before {
		width: 40%;
		height: $handle-height;
		bottom: 98%;
		left: 50%;
		margin-left: -20%;
		
		background: $col-blood;
	}
	
	&:after {
		width: 100%;
		height: 30px;
		top: -$handle-height - 25px;
		left: 0%;
		box-sizing: border-box;
		
		border: 10px solid $col-blood;
		border-radius: 4px 4px 20px 20px;
	}
}

JS部分：

(function() {
	function ready(fn) {
		if (document.readyState != 'loading'){
			fn();
		} else {
			document.addEventListener('DOMContentLoaded', fn);
		}
	}
	
	function makeSnow(el) {
		var ctx = el.getContext('2d');
		var width = 0;
		var height = 0;
		var particles = [];
		
		var Particle = function() {
			this.x = this.y = this.dx = this.dy = 0;
			this.reset();
		}
		
		Particle.prototype.reset = function() {
			this.y = Math.random() * height;
			this.x = Math.random() * width;
			this.dx = (Math.random() * 1) - 0.5;
			this.dy = (Math.random() * 0.5) + 0.5;
		}
		
		function createParticles(count) {
			if (count != particles.length) {
				particles = [];
				for (var i = 0; i < count; i++) {
					particles.push(new Particle());
				}
			}
		}
				
		function onResize() {
			width = window.innerWidth;
			height = window.innerHeight;
			el.width = width;
			el.height = height;
			
			createParticles((width * height) / 10000);
		}
		
		function updateParticles() {
			ctx.clearRect(0, 0, width, height);
			ctx.fillStyle = '#f6f9fa';
			
			particles.forEach(function(particle) {
				particle.y += particle.dy;
				particle.x += particle.dx;
				
				if (particle.y > height) {
					particle.y = 0;
				}
				
				if (particle.x > width) {
					particle.reset();
					particle.y = 0;
				}
				
				ctx.beginPath();
				ctx.arc(particle.x, particle.y, 5, 0, Math.PI * 2, false);
				ctx.fill();
			});
			
			window.requestAnimationFrame(updateParticles);
		}
		
		onResize();
		updateParticles();
		
		window.addEventListener('resize', onResize);
	}
	
	ready(function() {
		var canvas = document.getElementById('snow');
		makeSnow(canvas);
	});
})();