html - How do I vertically center text with CSS?

I have a div element which contains text, and I want to align the contents of this div vertically center.

Here is my div style:

#box {
  height: 170px;
  width: 270px;
  background: #000;
  font-size: 48px;
  color: #FFF;
  text-align: center;

}

  Lorem ipsum dolor sit

What is the best way to do this?