<h3>未知宽高的水平垂直居中</h3>
<h4>1、display:table-cell</h4>
<div class="box box1">
	<span>我是垂直<br>居中元素</span>
</div>
<h4>2、display:flex</h4>
<div class="box box2">
	<span>我是垂直居中元素</span>
</div>

<h4>3、translate(-50%,-50%)</h4>
<div class="box box3">
	<span>我是垂直居中元素</span>
</div>
<h4>4、display:inline-block</h4>
<div class="box box4">
	<span>我是垂直居中元素</span>
</div>
<h4>5、margin:auto</h4>
<div class="box box5">
	<span>我是垂直居中元素</span>
</div>
<h4>6、display:-webkit-box</h4>
<div class="box box6">
	<span>我是垂直居中元素</span>
</div>