<div class="alert_wapper">

    <div class="wapper">

        <!--内容 -->

    </div>

</div>

<style>

    .alert_wapper{

        position: fixed;

        top: 0;

        left: 0;

        right: 0;

        bottom: 0;

        width: 100%;

        height: 100%;

        background: rgba(0, 0, 0, 0.70);

        z-index: 99;

        overflow: auto;

    }

    .wapper{

        display: inline-block;

        &:after {

            display: block;

            content: ".";

            height: 0;

            line-height: 0;

            clear: both;

            visibility: hidden;

        }

    }

</style>