不固定高宽的 div 水平垂直居中

<div class="father">
	<div id="main"></div>
</div>

.father{
	position:fixed;
	width:100%;
	height:100%;
	/* top:0;
	left:0; */
}
#main{
	position: absolute;
	top:0;
	left:0;
	bottom:0;
	right:0;
	width:60%;
	height:60%;
	margin:auto;
}

https://www.haorooms.com/post/css_div_juzhong
https://www.cnblogs.com/zhangwenjiajessy/p/6130658.html