.block:before {
  content: '';
  display: inline-block;
  height: 100%;
  vertical-align: middle;
  margin-right: -0.25em; /* Adjusts for spacing */
}

/* The element to be centered, can
   also be of any width and height */
.centered {
  display: inline-block;
  vertical-align: middle;
  width: 300px;
}