SOURCE

<div class="block">
  <div class="content">
    伪元素法居中
  </div>
</div>

.block {
  height:300px;
  text-align:center;
  background: #d7d7d7;
}
.block:before {
  content: '';
  display: inline-block;
  height:100%;
  vertical-align: middle;
  margin-right:-0.25em;
}
.contend {
  display:inline-block;
  vertical-align:middle;
  width:50%;
}
.content {
  
}