基于vertical-align的纯CSS定位弹框

HTML

<div class="container">
    <div class="dialog">
        <div class="content">内容占位</div>
    </div>
</div>
<p>改变浏览器尺寸，或者修改内容尺寸可以发现弹框永远居中</p>
					    

CSS

.container {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAABtJREFUeNpiZGBgaGAgAjAxEAlGFVJHIUCAAQDcngCUgqGMqwAAAABJRU5ErkJggg==);
    background: rgba(0,0,0,.5), none;
    text-align: center;
    white-space: nowrap;
    font-size: 0;
    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;
    font-size: 14px;
    text-align: left;
    white-space: normal;
}
.content {
    width: 240px;
    height: 120px;
    padding: 20px;
}
				    

JS

//no