Аним. фон only css

только css. анимированный фон для примера портфолио.

by Denis Tverdokhlebov

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.1.3/css/bootstrap.min.css">
<body>	
	<div class="section-center">
		<div class="section-up">
			<div class="sun">
				<span></span>
			</div>
			<div class="cloud-left">
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div class="cloud-middle">
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div class="cloud-right">
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div class="bird-wrapper">
				<div class="left-wing">
					<span></span>
				</div>
				<div class="right-wing">
					<span></span>
				</div>
			</div>
			<div class="bird-wrapper snd">
				<div class="left-wing">
					<span></span>
				</div>
				<div class="right-wing">
					<span></span>
				</div>
			</div>
			<div class="bird-wrapper trd">
				<div class="left-wing">
					<span></span>
				</div>
				<div class="right-wing">
					<span></span>
				</div>
			</div>
			<div class="building-left">
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div class="building-right">
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span><span></span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div class="left-tree">
				<span></span>
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div class="right-tree">
				<span></span>
				<span></span>
				<span></span>
				<span></span>
				<span></span>
			</div>
			<div...

CSS

body{
	width: 100%;
	display: block;
	min-height: 100vh;
	background-color: #fee300;
}
.section-center{
	position: relative;
	width: 600px;
	height: 450px;
	display: block;
	z-index: 6;
	margin: 0 auto;
	overflow: hidden;
}
.section-up{
	position: absolute;
	width: 100%;
	height: 270px;
	left: 0;
	top: 0;
	display: block;
	z-index: 5;
}
.hill{
	position: absolute;
	width: 115px;
	height: 27px;
	left: 30px;
	bottom: 0;
	display: block;
	z-index: 15;
}
.hill.snd{
	left: 115px;
	z-index: 14;
}
.hill.trd{
	transform: rotateY(180deg);
	left: auto;
	right:30px;
}
.hill.frt{
	transform: rotateY(180deg);
	left: auto;
	right: 110px;
	z-index: 14;
}
.hill span{
	position: absolute;
	width: 60px;
	height: 60px;
	background-color: #fff;
	left: 4px;
	top: 0;
	display: block;
	border-radius: 50%;
	border: 2px solid #030308;
	border-color: #030308 transparent transparent transparent;
}
.hill span:nth-child(2){
	width: 110px;
	height: 110px;
	left: -6px;
	top: -5px;
	background-color: transparent;
	transform: rotate(5deg);
	border-color: transparent transparent transparent #030308;
}
.hill span:nth-child(3){
	width: 10px;
	height: 10px;
	left: 2px;
	top: 22px;
	transform: rotate(-55deg);
	border: none;
	border-radius: 0;
}
.hill span:nth-child(4){
	width: 40px;
	height: 40px;
	left: auto;
	top: 11px;
	right: 5px;
	border-color: #030308 transparent transparent transparent;
}
.hill span:nth-child(5){
	width: 110px;
	height: 110px;
	left: auto;
	top: 3px;
	right: -8px;
	background-color: transparent;
	transform: rotate(85deg);
	border-color: #030308 transparent transparent transparent;
}
.hill span:nth-child(6){
	width: 24px;
	height: 24px;
	left: auto;
	top: -5px;
	right: 31px;
	background-color: transparent;
	border-color: transparent transparent #030308 transparent;
}
.hill span:nth-child(7){
	width: 17px;
	height: 4px;
	left: auto;
	top: 10px;
	right: 49px;
	background-color: transparent;
	border-radius: 0;
	transform: rotate(33deg);
	border-color: #030308 transparent...