纯css实现弹窗左右垂直居中效果

<div class="container">
    <div class="dialog">
        <div class="content">内容占位</div>
    </div>
</div>

.container {
    position: fixed;
    top: 0; right: 0; bottom: 0; left: 0;
    /* for IE8 */
    background: url(data:image/png;base64,iVB...g==);
    /* for IE9+ */
    background: rgba(0,0,0,.5), none;
    text-align: center;
    white-space: nowrap;
    z-index: 99;
}
.container:after {
    content: "";
    display: inline-block;
    height: 100%;
    vertical-align: middle;
}
.dialog {
    display: inline-block;
    vertical-align: middle;
    border-radius: 6px;
    background-color: #fff;
    text-align: left;
    white-space: normal;
}