用户:你好/common.css

.blackbtn {
	position:fixed;
	margin:auto;
	left:0;
	right:0;
	top:0;
	bottom:0;
	background-color:black;
}
.opacity {
	opacity:0;
}
.div-relative {
    position:relative; 
    width:100%;
    height:100px
}

.div-a { 
    position:absolute; 
    width:auto;
    height:auto;
    left:50%;
    top:50%;
    transform:translate(-50%,-50%);
    animation-name: example;
    animation-duration: 1.5s;
    animation-iteration-count: infinite;
    animation-delay: -0.5s;
}
.div-b { 
    position:absolute;
    width:auto;
    height:auto;
    left:50%;
    top:50%;
    transform:translate(-50%,-50%);
    animation-name: example;
    animation-duration: 1.5s;
    animation-iteration-count: infinite;
    animation-delay: -1s;
}
.div-c { 
    position:absolute;
    width:auto;
    height:auto;
    left:50%;
    top:50%;
    transform:translate(-50%,-50%);
    animation-name: example;
    animation-duration: 1.5s;
    animation-iteration-count: infinite;
    animation-delay: -1.5s;
}
        @keyframes example {
  0%   {z-index:1;}
  33%  {z-index:-1;}
  66%  {z-index:-2;}
  100% {z-index:1;}
        }