loading加载动画

演示地址：https://xibushijie.github.io/loading/loading.html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no" />
    <style type="text/css">
 /* loading */
.loading {
    position: relative;
}
 
.loading::before {
     4px; height: 4px;
    margin: auto;
    content: '';
    -webkit-animation: spinZoom 1s steps(8) infinite;
    animation: spinZoom 1s steps(8) infinite;
    border-radius: 100%;
    box-shadow: 0 -10px 0 1px currentColor, 10px 0 currentColor, 0 10px currentColor, -10px 0 currentColor, -7px -7px 0 .5px currentColor, 7px -7px 0 1.5px currentColor, 7px 7px currentColor, -7px 7px currentColor;
    /* center */
    position: absolute;
    top: 0; right: 0; bottom: 0; left: 0;
}
/* loading动画 */
@-webkit-keyframes spinZoom {
    0% {
        -webkit-transform: scale(.75) rotate(0);
    }
    100% {
        -webkit-transform: scale(.75) rotate(360deg);
    }
}
@keyframes spinZoom {
    0% {
        transform: scale(.75) rotate(0);
    }
    100% {
        transform: scale(.75) rotate(360deg);
    }
}
    </style>
</head>
<body>
    <a href="" class="btn loading"> </a>
</body>
</html>