html,body { height: 100%; margin: 0; }
.loading { 
    position: absolute; z-index: 9999;
    top: 0; left: 0;
    width: 100%; height: 100%;
    display: none;
}
.loading .mask {
    position:  absolute;
    width: 100%; height: 100%;
    background-color: #444; opacity: 0.5;
}
.loading .animation {
    width: 64px; height: 64px;
    margin: auto; margin-top: 40px;
    background: url('https://i.imgur.com/6pCtQAW.gif');
}