<div class="wrap">
  <div class="child">
    I'm am element in inline-block. I have the very long content in me. And I may be occup more lines in some situation.
  </div>
</div>
body {
  background: #f06d06;
  padding-top: 40px;
}
.wrap {
  background: #fff;
  border-radius: 5px;
  width: 300px;
  height: 300px;
  margin: 0 auto;
  text-align: center;
}
.wrap::before {
  display: inline-block;
  vertical-align: middle;
  content: '';
  height: 100%;
  width: 0;
}
.child {
  display: inline-block;
  vertical-align: middle;
  width: 150px;
  color: #666;
}

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