飘屏动画

    <div class="a">1123132123</div>
    <div class="img-box"></div>

	body{
		background: black;
		/* overflow: hidden; */
		height: 10000px;
	}
	.img-box{
		top: 0;
		left: 0;
		position: fixed;
		z-index: 999;
	}
	img{
		position: absolute;
	}
	.a{
		width: 100px;
		height: 100px;
		background: aquamarine;
	}

	setInterval(function(){
		//创建雪花图片
		const snow = $('<img src="../img/snow.png">');
		//得到窗口的宽高
		const width = document.documentElement.clientWidth;
		const height = document.documentElement.clientHeight;
		//设置随机雪花宽高0-14
		const size = Math.floor(Math.random()*5+12)+'px';
		//设置随机的横向位置
		const left = Math.floor(Math.random()*width)+'px';
		//设置css样式
		snow.css({'width':size,'height':size,'left':left,'top':0});
		//添加到body中
		$('.img-box').append(snow);
		//让图片移动到窗口最下面
		const time = Math.floor(Math.random()*5000)+3000;
		//让图片落下后过一段时间消失
		snow.animate({'top':(height-parseInt(size))+'px'},time).fadeOut(1000,function(){$(this).remove()});
	},100);