弹窗、遮罩层

.mask,.alert{display:none;position:fixed;top:0;left:0;width:100%;height:100%;}
.mask{background-color:#000;opacity:.6;filter:alpha(opacity=60);z-index:998;}
.alert{display:flex;justify-content:center;align-items:center;visibility:hidden;z-index:1000;}/*移动端居中*/
.alert-content{background:#fff;box-shadow:0 0 5px 2px rgba(0,0,0,.3);padding:10px;border-radius:10px;margin:0 15px;}