html,
body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
}
.vertical-middle-block {
  position: relative;
  text-align: center;
  background: #c0c0c0;
  margin: 0;
  height: 100%;
}
.vertical-middle-block:before {
  content: '';
  display: inline-block;
  height: 100%;
  vertical-align: middle;
  margin-right: -0.25em;
  /* Adjusts for spacing */

  /* For visualization 
    background: #808080; width: 5px;
    */

  overflow: hidden;
}
.centered {
  display: inline-block;
  vertical-align: middle;
  width: 300px;
  padding: 10px 15px;
  border: #a0a0a0 solid 1px;
  background: #f5f5f5;
}