SOURCE

<div class="loading">
		<span></span>
		<span></span>
		<span></span>
		<span></span>
		<span></span>
</div>

.loading{
	width: 80px;
	height: 40px;
	margin: 0 auto;
	margin-top:100px;
}
.loading span{
	display: inline-block;
	width: 8px;                /* display:inline-block的默认间距是多少？ */
	height: 100%;
	border-radius: 4px;
	background: lightgreen;
	-webkit-animation: load 1s ease infinite;
}
@-webkit-keyframes load{
	0%,100%{
		height: 40px;
		background: lightgreen;
	}
	50%{
		height: 70px;
		margin: -15px 0;       /* 负值的原理？  */
		background: lightblue;
}
}
.loading span:nth-child(2){
	-webkit-animation-delay:0.2s;
}
.loading span:nth-child(3){
	-webkit-animation-delay:0.4s;
}
.loading span:nth-child(4){
	-webkit-animation-delay:0.6s;
}
.loading span:nth-child(5){
	-webkit-animation-delay:0.8s;
}